Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Sakari Ailus]

Hi Marek,

On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
> Hi Laurent,
> 
> On 2017-04-20 12:25, Laurent Pinchart wrote:
> >Hi Marek,
> >
> >(CC'ing Sakari Ailus)
> >
> >Thank you for the patches.
> >
> >On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
> >>Dear all,
> >>
> >>This is an updated proposal for extending EXYNOS DRM API with generic
> >>support for hardware modules, which can be used for processing image data
> >>from the one memory buffer to another. Typical memory-to-memory operations
> >>are: rotation, scaling, colour space conversion or mix of them. This is a
> >>follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
> >>processors", which has been rejected as "not really needed in the DRM
> >>core":
> >>http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
> >>
> >>In this proposal I moved all the code to Exynos DRM driver, so now this
> >>will be specific only to Exynos DRM. I've also changed the name from
> >>framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
> >>with fbdev API.
> >>
> >>Here is a bit more information what picture processors are:
> >>
> >>Embedded SoCs are known to have a number of hardware blocks, which perform
> >>such operations. They can be used in paralel to the main GPU module to
> >>offload CPU from processing grapics or video data. One of example use of
> >>such modules is implementing video overlay, which usually requires color
> >>space conversion from NV12 (or similar) to RGB32 color space and scaling to
> >>target window size.
> >>
> >>The proposed API is heavily inspired by atomic KMS approach - it is also
> >>based on DRM objects and their properties. A new DRM object is introduced:
> >>picture processor (called pp for convenience). Such objects have a set of
> >>standard DRM properties, which describes the operation to be performed by
> >>respective hardware module. In typical case those properties are a source
> >>fb id and rectangle (x, y, width, height) and destination fb id and
> >>rectangle. Optionally a rotation property can be also specified if
> >>supported by the given hardware. To perform an operation on image data,
> >>userspace provides a set of properties and their values for given fbproc
> >>object in a similar way as object and properties are provided for
> >>performing atomic page flip / mode setting.
> >>
> >>The proposed API consists of the 3 new ioctls:
> >>- DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
> >>   processors,
> >>- DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
> >>   processor,
> >>- DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
> >>   property set.
> >>
> >>The proposed API is extensible. Drivers can attach their own, custom
> >>properties to add support for more advanced picture processing (for example
> >>blending).
> >>
> >>This proposal aims to replace Exynos DRM IPP (Image Post Processing)
> >>subsystem. IPP API is over-engineered in general, but not really extensible
> >>on the other side. It is also buggy, with significant design flaws - the
> >>biggest issue is the fact that the API covers memory-2-memory picture
> >>operations together with CRTC writeback and duplicating features, which
> >>belongs to video plane. Comparing with IPP subsystem, the PP framework is
> >>smaller (1807 vs 778 lines) and allows driver simplification (Exynos
> >>rotator driver smaller by over 200 lines).
> >This seems to be the kind of hardware that is typically supported by V4L2.
> >Stupid question, why DRM ?
> 
> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
> 
> 1. we want to replace existing Exynos IPP subsystem:
>  - it is used only in some internal/vendor trees, not in open-source
>  - we want it to have sane and potentially extensible userspace API
>  - but we don't want to loose its functionality
> 
> 2. we want to have simple API for performing single image processing
> operation:
>  - typically it will be used by compositing window manager, this means that
>    some parameters of the processing might change on each vblank (like
>    destination rectangle for example). This api allows such change on each
>    operation without any additional cost. V4L2 requires to reinitialize
>    queues with new configuration on such change, what means that a bunch of
>    ioctls has to be called.

What do you mean by re-initialising the queue? Format, buffers or something
else?

If you need a larger buffer than what you have already allocated, you'll
need to re-allocate, V4L2 or not.

We also do lack a way to destroy individual buffers in V4L2. It'd be up to
implementing that and some work in videobuf2.

Another thing is that V4L2 is very stream oriented. For most devices that's
fine as a lot of the parameters are not changeable during streaming,
especially if the pipeline is handled by multiple drivers. That said, for
devices that process data from memory to memory performing changes in the
media bus formats and pipeline configuration is not very efficient
currently, largely for the same reason.

The request API that people have been working for a bit different use cases
isn't in mainline yet. It would allow more efficient per-request
configuration than what is currently possible, but it has turned out to be
far from trivial to implement.

>  - validating processing parameters in V4l2 API is really complicated,
>    because the parameters (format, src&dest rectangles, rotation) are being
>    set incrementally, so we have to either allow some impossible,
> transitional
>    configurations or complicate the configuration steps even more (like
>    calling some ioctls multiple times for both input and output). In the end
>    all parameters have to be again validated just before performing the
>    operation.

You have to validate the parameters in any case. In a MC pipeline this takes
place when the stream is started.

> 
> 3. generic approach (to add it to DRM core) has been rejected:
> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html

For GPUs I generally understand the reasoning: there's a very limited number
of users of this API --- primarily because it's not an application
interface.

If you have a device that however falls under the scope of V4L2 (at least
API-wise), does this continue to be the case? Will there be only one or two
(or so) users for this API? Is it the case here?

Using a device specific interface definitely has some benefits: there's no
need to think how would you generalise the interface for other similar
devices. There's no need to consider backwards compatibility as it's not a
requirement. The drawback is that the applications that need to support
similar devices will bear the burden of having to support different APIs.

I don't mean to say that you should ram whatever under V4L2 / MC
independently of how unworkable that might be, but there are also clear
advantages in using a standardised interface such as V4L2.

V4L2 has a long history behind it and if it was designed today, I bet it
would look quite different from what it is now.

> 
> 4. this api can be considered as extended 'blit' operation, other DRM
> drivers
>    (MGA, R128, VIA) already have ioctls for such operation, so there is also
>    place in DRM for it

Added LMML to cc.

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@iki.fi	XMPP: sailus@retiisi.org.uk

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Nicolas Dufresne]

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Le mercredi 26 avril 2017 à 01:21 +0300, Sakari Ailus a écrit :
> Hi Marek,
> 
> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
> > Hi Laurent,
> > 
> > On 2017-04-20 12:25, Laurent Pinchart wrote:
> > > Hi Marek,
> > > 
> > > (CC'ing Sakari Ailus)
> > > 
> > > Thank you for the patches.
> > > 
> > > On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
> > > > Dear all,
> > > > 
> > > > This is an updated proposal for extending EXYNOS DRM API with generic
> > > > support for hardware modules, which can be used for processing image data
> > > > from the one memory buffer to another. Typical memory-to-memory operations
> > > > are: rotation, scaling, colour space conversion or mix of them. This is a
> > > > follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
> > > > processors", which has been rejected as "not really needed in the DRM
> > > > core":
> > > > http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
> > > > 
> > > > In this proposal I moved all the code to Exynos DRM driver, so now this
> > > > will be specific only to Exynos DRM. I've also changed the name from
> > > > framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
> > > > with fbdev API.
> > > > 
> > > > Here is a bit more information what picture processors are:
> > > > 
> > > > Embedded SoCs are known to have a number of hardware blocks, which perform
> > > > such operations. They can be used in paralel to the main GPU module to
> > > > offload CPU from processing grapics or video data. One of example use of
> > > > such modules is implementing video overlay, which usually requires color
> > > > space conversion from NV12 (or similar) to RGB32 color space and scaling to
> > > > target window size.
> > > > 
> > > > The proposed API is heavily inspired by atomic KMS approach - it is also
> > > > based on DRM objects and their properties. A new DRM object is introduced:
> > > > picture processor (called pp for convenience). Such objects have a set of
> > > > standard DRM properties, which describes the operation to be performed by
> > > > respective hardware module. In typical case those properties are a source
> > > > fb id and rectangle (x, y, width, height) and destination fb id and
> > > > rectangle. Optionally a rotation property can be also specified if
> > > > supported by the given hardware. To perform an operation on image data,
> > > > userspace provides a set of properties and their values for given fbproc
> > > > object in a similar way as object and properties are provided for
> > > > performing atomic page flip / mode setting.
> > > > 
> > > > The proposed API consists of the 3 new ioctls:
> > > > - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
> > > >   processors,
> > > > - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
> > > >   processor,
> > > > - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
> > > >   property set.
> > > > 
> > > > The proposed API is extensible. Drivers can attach their own, custom
> > > > properties to add support for more advanced picture processing (for example
> > > > blending).
> > > > 
> > > > This proposal aims to replace Exynos DRM IPP (Image Post Processing)
> > > > subsystem. IPP API is over-engineered in general, but not really extensible
> > > > on the other side. It is also buggy, with significant design flaws - the
> > > > biggest issue is the fact that the API covers memory-2-memory picture
> > > > operations together with CRTC writeback and duplicating features, which
> > > > belongs to video plane. Comparing with IPP subsystem, the PP framework is
> > > > smaller (1807 vs 778 lines) and allows driver simplification (Exynos
> > > > rotator driver smaller by over 200 lines).

Just a side note, we have written code in GStreamer using the Exnynos 4
FIMC IPP driver. I don't know how many, if any, deployment still exist
(Exynos 4 is relatively old now), but there exist userspace for the
FIMC driver. We use this for color transformation (from tiled to
linear) and scaling. The FIMC driver is in fact quite stable in
upstream kernel today. The GScaler V4L2 M2M driver on Exynos 5 is
largely based on it and has received some maintenance to properly work
in GStreamer. unlike this DRM API, you can reuse the same userspace
code across multiple platforms (which we do already). We have also
integrated this driver in Chromium in the past (not upstream though).

I am well aware that the blitter driver has not got much attention
though. But again, V4L2 offers a generic interface to userspace
application. Fixing this driver could enable some work like this one:

https://bugzilla.gnome.org/show_bug.cgi?id=772766

This work in progress feature is a generic hardware accelerated video
mixer. It has been tested with IMX.6 v4l2 m2m blitter driver (which I
believe is in staging right now). Again, unlike the exynos/drm, this
code could be reused between platforms.

In general, the problem with the DRM approach is that it only targets
displays. We often need to use these IP block for stream pre/post
processing outside a "playback" use case.

What I'd like so see instead here, is an approach that helps both world
 instead of trying to win the control over the IP block. Renesas
development seems to lead toward the right direction by creating
drivers that can be both interfaced in DRM and V4L2. For IPP and
GScaler on Exynos, this would be a greater benefit and finally the code
could be shared, having a single place to fix when we find bugs.

> > > 
> > > This seems to be the kind of hardware that is typically supported by V4L2.
> > > Stupid question, why DRM ?
> > 
> > Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
> > 
> > 1. we want to replace existing Exynos IPP subsystem:
> >  - it is used only in some internal/vendor trees, not in open-source
> >  - we want it to have sane and potentially extensible userspace API
> >  - but we don't want to loose its functionality
> > 
> > 2. we want to have simple API for performing single image processing
> > operation:
> >  - typically it will be used by compositing window manager, this means that
> >    some parameters of the processing might change on each vblank (like
> >    destination rectangle for example). This api allows such change on each
> >    operation without any additional cost. V4L2 requires to reinitialize
> >    queues with new configuration on such change, what means that a bunch of
> >    ioctls has to be called.
> 
> What do you mean by re-initialising the queue? Format, buffers or something
> else?
> 
> If you need a larger buffer than what you have already allocated, you'll
> need to re-allocate, V4L2 or not.
> 
> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
> implementing that and some work in videobuf2.
> 
> Another thing is that V4L2 is very stream oriented. For most devices that's
> fine as a lot of the parameters are not changeable during streaming,
> especially if the pipeline is handled by multiple drivers. That said, for
> devices that process data from memory to memory performing changes in the
> media bus formats and pipeline configuration is not very efficient
> currently, largely for the same reason.
> 
> The request API that people have been working for a bit different use cases
> isn't in mainline yet. It would allow more efficient per-request
> configuration than what is currently possible, but it has turned out to be
> far from trivial to implement.
> 
> >  - validating processing parameters in V4l2 API is really complicated,
> >    because the parameters (format, src&dest rectangles, rotation) are being
> >    set incrementally, so we have to either allow some impossible,
> > transitional
> >    configurations or complicate the configuration steps even more (like
> >    calling some ioctls multiple times for both input and output). In the end
> >    all parameters have to be again validated just before performing the
> >    operation.
> 
> You have to validate the parameters in any case. In a MC pipeline this takes
> place when the stream is started.
> 
> > 
> > 3. generic approach (to add it to DRM core) has been rejected:
> > http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
> 
> For GPUs I generally understand the reasoning: there's a very limited number
> of users of this API --- primarily because it's not an application
> interface.
> 
> If you have a device that however falls under the scope of V4L2 (at least
> API-wise), does this continue to be the case? Will there be only one or two
> (or so) users for this API? Is it the case here?
> 
> Using a device specific interface definitely has some benefits: there's no
> need to think how would you generalise the interface for other similar
> devices. There's no need to consider backwards compatibility as it's not a
> requirement. The drawback is that the applications that need to support
> similar devices will bear the burden of having to support different APIs.
> 
> I don't mean to say that you should ram whatever under V4L2 / MC
> independently of how unworkable that might be, but there are also clear
> advantages in using a standardised interface such as V4L2.
> 
> V4L2 has a long history behind it and if it was designed today, I bet it
> would look quite different from what it is now.
> 
> > 
> > 4. this api can be considered as extended 'blit' operation, other DRM
> > drivers
> >    (MGA, R128, VIA) already have ioctls for such operation, so there is also
> >    place in DRM for it

Note that I am convince that using these custom IOCTL within a
"compositor" implementation is much easier and uniform compared to
using a v4l2 driver. It probably offers lower latency. But these are
non-generic and are not a great fit for streaming purpose. Request API
and probably explicit fence may mitigate this though. Meanwhile, there
is some indication that even though complex, there is already some
people that do think implementing a compositor combining V4L2 and DRM
is feasible.

http://events.linuxfoundation.org/sites/events/files/slides/als2015_way
land_weston_v2.pdf

> 
> Added LMML to cc.

Thanks.

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Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Tobias Jakobi]

Hello everyone,


Nicolas Dufresne wrote:
> Le mercredi 26 avril 2017 à 01:21 +0300, Sakari Ailus a écrit :
>> Hi Marek,
>>
>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>>> Hi Laurent,
>>>
>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>>> Hi Marek,
>>>>
>>>> (CC'ing Sakari Ailus)
>>>>
>>>> Thank you for the patches.
>>>>
>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>>> Dear all,
>>>>>
>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>>> support for hardware modules, which can be used for processing image data
>>>>> from the one memory buffer to another. Typical memory-to-memory operations
>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>>> processors", which has been rejected as "not really needed in the DRM
>>>>> core":
>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>
>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>>> with fbdev API.
>>>>>
>>>>> Here is a bit more information what picture processors are:
>>>>>
>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>>> such operations. They can be used in paralel to the main GPU module to
>>>>> offload CPU from processing grapics or video data. One of example use of
>>>>> such modules is implementing video overlay, which usually requires color
>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>>> target window size.
>>>>>
>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>>> picture processor (called pp for convenience). Such objects have a set of
>>>>> standard DRM properties, which describes the operation to be performed by
>>>>> respective hardware module. In typical case those properties are a source
>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>>> rectangle. Optionally a rotation property can be also specified if
>>>>> supported by the given hardware. To perform an operation on image data,
>>>>> userspace provides a set of properties and their values for given fbproc
>>>>> object in a similar way as object and properties are provided for
>>>>> performing atomic page flip / mode setting.
>>>>>
>>>>> The proposed API consists of the 3 new ioctls:
>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>>   processors,
>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>>   processor,
>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>>   property set.
>>>>>
>>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>>> properties to add support for more advanced picture processing (for example
>>>>> blending).
>>>>>
>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>>> on the other side. It is also buggy, with significant design flaws - the
>>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>>> operations together with CRTC writeback and duplicating features, which
>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>>> rotator driver smaller by over 200 lines).
> 
> Just a side note, we have written code in GStreamer using the Exnynos 4
> FIMC IPP driver. I don't know how many, if any, deployment still exist
> (Exynos 4 is relatively old now), but there exist userspace for the
> FIMC driver. We use this for color transformation (from tiled to
> linear) and scaling. The FIMC driver is in fact quite stable in
> upstream kernel today. The GScaler V4L2 M2M driver on Exynos 5 is
> largely based on it and has received some maintenance to properly work
> in GStreamer. unlike this DRM API, you can reuse the same userspace
> code across multiple platforms (which we do already). We have also
> integrated this driver in Chromium in the past (not upstream though).
> 
> I am well aware that the blitter driver has not got much attention
> though. But again, V4L2 offers a generic interface to userspace
> application. Fixing this driver could enable some work like this one:
> 
> https://bugzilla.gnome.org/show_bug.cgi?id=772766
> 
> This work in progress feature is a generic hardware accelerated video
> mixer. It has been tested with IMX.6 v4l2 m2m blitter driver (which I
> believe is in staging right now). Again, unlike the exynos/drm, this
> code could be reused between platforms.
> 
> In general, the problem with the DRM approach is that it only targets
> displays. We often need to use these IP block for stream pre/post
> processing outside a "playback" use case.
just a short note that this is not true. You can use all this
functionality e.g. through render nodes, without needing to have a
display attached to your system.

With best wishes,
Tobias


> What I'd like so see instead here, is an approach that helps both world
>  instead of trying to win the control over the IP block. Renesas
> development seems to lead toward the right direction by creating
> drivers that can be both interfaced in DRM and V4L2. For IPP and
> GScaler on Exynos, this would be a greater benefit and finally the code
> could be shared, having a single place to fix when we find bugs.
> 
>>>>
>>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>>> Stupid question, why DRM ?
>>>
>>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>>
>>> 1. we want to replace existing Exynos IPP subsystem:
>>>  - it is used only in some internal/vendor trees, not in open-source
>>>  - we want it to have sane and potentially extensible userspace API
>>>  - but we don't want to loose its functionality
>>>
>>> 2. we want to have simple API for performing single image processing
>>> operation:
>>>  - typically it will be used by compositing window manager, this means that
>>>    some parameters of the processing might change on each vblank (like
>>>    destination rectangle for example). This api allows such change on each
>>>    operation without any additional cost. V4L2 requires to reinitialize
>>>    queues with new configuration on such change, what means that a bunch of
>>>    ioctls has to be called.
>>
>> What do you mean by re-initialising the queue? Format, buffers or something
>> else?
>>
>> If you need a larger buffer than what you have already allocated, you'll
>> need to re-allocate, V4L2 or not.
>>
>> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
>> implementing that and some work in videobuf2.
>>
>> Another thing is that V4L2 is very stream oriented. For most devices that's
>> fine as a lot of the parameters are not changeable during streaming,
>> especially if the pipeline is handled by multiple drivers. That said, for
>> devices that process data from memory to memory performing changes in the
>> media bus formats and pipeline configuration is not very efficient
>> currently, largely for the same reason.
>>
>> The request API that people have been working for a bit different use cases
>> isn't in mainline yet. It would allow more efficient per-request
>> configuration than what is currently possible, but it has turned out to be
>> far from trivial to implement.
>>
>>>  - validating processing parameters in V4l2 API is really complicated,
>>>    because the parameters (format, src&dest rectangles, rotation) are being
>>>    set incrementally, so we have to either allow some impossible,
>>> transitional
>>>    configurations or complicate the configuration steps even more (like
>>>    calling some ioctls multiple times for both input and output). In the end
>>>    all parameters have to be again validated just before performing the
>>>    operation.
>>
>> You have to validate the parameters in any case. In a MC pipeline this takes
>> place when the stream is started.
>>
>>>
>>> 3. generic approach (to add it to DRM core) has been rejected:
>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>
>> For GPUs I generally understand the reasoning: there's a very limited number
>> of users of this API --- primarily because it's not an application
>> interface.
>>
>> If you have a device that however falls under the scope of V4L2 (at least
>> API-wise), does this continue to be the case? Will there be only one or two
>> (or so) users for this API? Is it the case here?
>>
>> Using a device specific interface definitely has some benefits: there's no
>> need to think how would you generalise the interface for other similar
>> devices. There's no need to consider backwards compatibility as it's not a
>> requirement. The drawback is that the applications that need to support
>> similar devices will bear the burden of having to support different APIs.
>>
>> I don't mean to say that you should ram whatever under V4L2 / MC
>> independently of how unworkable that might be, but there are also clear
>> advantages in using a standardised interface such as V4L2.
>>
>> V4L2 has a long history behind it and if it was designed today, I bet it
>> would look quite different from what it is now.
>>
>>>
>>> 4. this api can be considered as extended 'blit' operation, other DRM
>>> drivers
>>>    (MGA, R128, VIA) already have ioctls for such operation, so there is also
>>>    place in DRM for it
> 
> Note that I am convince that using these custom IOCTL within a
> "compositor" implementation is much easier and uniform compared to
> using a v4l2 driver. It probably offers lower latency. But these are
> non-generic and are not a great fit for streaming purpose. Request API
> and probably explicit fence may mitigate this though. Meanwhile, there
> is some indication that even though complex, there is already some
> people that do think implementing a compositor combining V4L2 and DRM
> is feasible.
> 
> http://events.linuxfoundation.org/sites/events/files/slides/als2015_way
> land_weston_v2.pdf
> 
>>
>> Added LMML to cc.
> 
> Thanks.
> 

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Marek Szyprowski]

Hi Tobias and Nicolas,

On 2017-04-26 17:16, Tobias Jakobi wrote:
> Nicolas Dufresne wrote:
>> Le mercredi 26 avril 2017 à 01:21 +0300, Sakari Ailus a écrit :
>>> Hi Marek,
>>>
>>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>>>> Hi Laurent,
>>>>
>>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>>>> Hi Marek,
>>>>>
>>>>> (CC'ing Sakari Ailus)
>>>>>
>>>>> Thank you for the patches.
>>>>>
>>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>>>> Dear all,
>>>>>>
>>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>>>> support for hardware modules, which can be used for processing image data
>>>>>> from the one memory buffer to another. Typical memory-to-memory operations
>>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>>>> processors", which has been rejected as "not really needed in the DRM
>>>>>> core":
>>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>>
>>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>>>> with fbdev API.
>>>>>>
>>>>>> Here is a bit more information what picture processors are:
>>>>>>
>>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>>>> such operations. They can be used in paralel to the main GPU module to
>>>>>> offload CPU from processing grapics or video data. One of example use of
>>>>>> such modules is implementing video overlay, which usually requires color
>>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>>>> target window size.
>>>>>>
>>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>>>> picture processor (called pp for convenience). Such objects have a set of
>>>>>> standard DRM properties, which describes the operation to be performed by
>>>>>> respective hardware module. In typical case those properties are a source
>>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>>>> rectangle. Optionally a rotation property can be also specified if
>>>>>> supported by the given hardware. To perform an operation on image data,
>>>>>> userspace provides a set of properties and their values for given fbproc
>>>>>> object in a similar way as object and properties are provided for
>>>>>> performing atomic page flip / mode setting.
>>>>>>
>>>>>> The proposed API consists of the 3 new ioctls:
>>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>>>    processors,
>>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>>>    processor,
>>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>>>    property set.
>>>>>>
>>>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>>>> properties to add support for more advanced picture processing (for example
>>>>>> blending).
>>>>>>
>>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>>>> on the other side. It is also buggy, with significant design flaws - the
>>>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>>>> operations together with CRTC writeback and duplicating features, which
>>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>>>> rotator driver smaller by over 200 lines).
>> Just a side note, we have written code in GStreamer using the Exnynos 4
>> FIMC IPP driver. I don't know how many, if any, deployment still exist
>> (Exynos 4 is relatively old now), but there exist userspace for the
>> FIMC driver. We use this for color transformation (from tiled to
>> linear) and scaling. The FIMC driver is in fact quite stable in
>> upstream kernel today. The GScaler V4L2 M2M driver on Exynos 5 is
>> largely based on it and has received some maintenance to properly work
>> in GStreamer. unlike this DRM API, you can reuse the same userspace
>> code across multiple platforms (which we do already). We have also
>> integrated this driver in Chromium in the past (not upstream though).
>>
>> I am well aware that the blitter driver has not got much attention
>> though. But again, V4L2 offers a generic interface to userspace
>> application. Fixing this driver could enable some work like this one:
>>
>> https://bugzilla.gnome.org/show_bug.cgi?id=772766
>>
>> This work in progress feature is a generic hardware accelerated video
>> mixer. It has been tested with IMX.6 v4l2 m2m blitter driver (which I
>> believe is in staging right now). Again, unlike the exynos/drm, this
>> code could be reused between platforms.
>>
>> In general, the problem with the DRM approach is that it only targets
>> displays. We often need to use these IP block for stream pre/post
>> processing outside a "playback" use case.
> just a short note that this is not true. You can use all this
> functionality e.g. through render nodes, without needing to have a
> display attached to your system.

Yes. As an alternative I also plan to provide generic V4L2-style mem2mem
device on top of this Exynos DRM interface. This will also help on the newer
Exynos SoCs, which even don't have GScaller. This way we can also easily get
rid of two drivers for GScaller hw. FIMC will probably stay in V4L2 because
of its camera related functions.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Tobias Jakobi]

Hello again,


Nicolas Dufresne wrote:
> Le mercredi 26 avril 2017 à 01:21 +0300, Sakari Ailus a écrit :
>> Hi Marek,
>>
>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>>> Hi Laurent,
>>>
>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>>> Hi Marek,
>>>>
>>>> (CC'ing Sakari Ailus)
>>>>
>>>> Thank you for the patches.
>>>>
>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>>> Dear all,
>>>>>
>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>>> support for hardware modules, which can be used for processing image data
>>>>> from the one memory buffer to another. Typical memory-to-memory operations
>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>>> processors", which has been rejected as "not really needed in the DRM
>>>>> core":
>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>
>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>>> with fbdev API.
>>>>>
>>>>> Here is a bit more information what picture processors are:
>>>>>
>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>>> such operations. They can be used in paralel to the main GPU module to
>>>>> offload CPU from processing grapics or video data. One of example use of
>>>>> such modules is implementing video overlay, which usually requires color
>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>>> target window size.
>>>>>
>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>>> picture processor (called pp for convenience). Such objects have a set of
>>>>> standard DRM properties, which describes the operation to be performed by
>>>>> respective hardware module. In typical case those properties are a source
>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>>> rectangle. Optionally a rotation property can be also specified if
>>>>> supported by the given hardware. To perform an operation on image data,
>>>>> userspace provides a set of properties and their values for given fbproc
>>>>> object in a similar way as object and properties are provided for
>>>>> performing atomic page flip / mode setting.
>>>>>
>>>>> The proposed API consists of the 3 new ioctls:
>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>>   processors,
>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>>   processor,
>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>>   property set.
>>>>>
>>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>>> properties to add support for more advanced picture processing (for example
>>>>> blending).
>>>>>
>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>>> on the other side. It is also buggy, with significant design flaws - the
>>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>>> operations together with CRTC writeback and duplicating features, which
>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>>> rotator driver smaller by over 200 lines).
> 
> Just a side note, we have written code in GStreamer using the Exnynos 4
> FIMC IPP driver. I don't know how many, if any, deployment still exist
> (Exynos 4 is relatively old now), but there exist userspace for the
> FIMC driver.
I was searching for this code, but I didn't find anything. Are you sure
you really mean the FIMC IPP in Exynos DRM, and not just the FIMC driver
from the V4L2 subsystem?


With best wishes,
Tobias



> We use this for color transformation (from tiled to
> linear) and scaling. The FIMC driver is in fact quite stable in
> upstream kernel today. The GScaler V4L2 M2M driver on Exynos 5 is
> largely based on it and has received some maintenance to properly work
> in GStreamer. unlike this DRM API, you can reuse the same userspace
> code across multiple platforms (which we do already). We have also
> integrated this driver in Chromium in the past (not upstream though).
> 
> I am well aware that the blitter driver has not got much attention
> though. But again, V4L2 offers a generic interface to userspace
> application. Fixing this driver could enable some work like this one:
> 
> https://bugzilla.gnome.org/show_bug.cgi?id=772766
> 
> This work in progress feature is a generic hardware accelerated video
> mixer. It has been tested with IMX.6 v4l2 m2m blitter driver (which I
> believe is in staging right now). Again, unlike the exynos/drm, this
> code could be reused between platforms.
> 
> In general, the problem with the DRM approach is that it only targets
> displays. We often need to use these IP block for stream pre/post
> processing outside a "playback" use case.
> 
> What I'd like so see instead here, is an approach that helps both world
>  instead of trying to win the control over the IP block. Renesas
> development seems to lead toward the right direction by creating
> drivers that can be both interfaced in DRM and V4L2. For IPP and
> GScaler on Exynos, this would be a greater benefit and finally the code
> could be shared, having a single place to fix when we find bugs.
> 
>>>>
>>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>>> Stupid question, why DRM ?
>>>
>>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>>
>>> 1. we want to replace existing Exynos IPP subsystem:
>>>  - it is used only in some internal/vendor trees, not in open-source
>>>  - we want it to have sane and potentially extensible userspace API
>>>  - but we don't want to loose its functionality
>>>
>>> 2. we want to have simple API for performing single image processing
>>> operation:
>>>  - typically it will be used by compositing window manager, this means that
>>>    some parameters of the processing might change on each vblank (like
>>>    destination rectangle for example). This api allows such change on each
>>>    operation without any additional cost. V4L2 requires to reinitialize
>>>    queues with new configuration on such change, what means that a bunch of
>>>    ioctls has to be called.
>>
>> What do you mean by re-initialising the queue? Format, buffers or something
>> else?
>>
>> If you need a larger buffer than what you have already allocated, you'll
>> need to re-allocate, V4L2 or not.
>>
>> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
>> implementing that and some work in videobuf2.
>>
>> Another thing is that V4L2 is very stream oriented. For most devices that's
>> fine as a lot of the parameters are not changeable during streaming,
>> especially if the pipeline is handled by multiple drivers. That said, for
>> devices that process data from memory to memory performing changes in the
>> media bus formats and pipeline configuration is not very efficient
>> currently, largely for the same reason.
>>
>> The request API that people have been working for a bit different use cases
>> isn't in mainline yet. It would allow more efficient per-request
>> configuration than what is currently possible, but it has turned out to be
>> far from trivial to implement.
>>
>>>  - validating processing parameters in V4l2 API is really complicated,
>>>    because the parameters (format, src&dest rectangles, rotation) are being
>>>    set incrementally, so we have to either allow some impossible,
>>> transitional
>>>    configurations or complicate the configuration steps even more (like
>>>    calling some ioctls multiple times for both input and output). In the end
>>>    all parameters have to be again validated just before performing the
>>>    operation.
>>
>> You have to validate the parameters in any case. In a MC pipeline this takes
>> place when the stream is started.
>>
>>>
>>> 3. generic approach (to add it to DRM core) has been rejected:
>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>
>> For GPUs I generally understand the reasoning: there's a very limited number
>> of users of this API --- primarily because it's not an application
>> interface.
>>
>> If you have a device that however falls under the scope of V4L2 (at least
>> API-wise), does this continue to be the case? Will there be only one or two
>> (or so) users for this API? Is it the case here?
>>
>> Using a device specific interface definitely has some benefits: there's no
>> need to think how would you generalise the interface for other similar
>> devices. There's no need to consider backwards compatibility as it's not a
>> requirement. The drawback is that the applications that need to support
>> similar devices will bear the burden of having to support different APIs.
>>
>> I don't mean to say that you should ram whatever under V4L2 / MC
>> independently of how unworkable that might be, but there are also clear
>> advantages in using a standardised interface such as V4L2.
>>
>> V4L2 has a long history behind it and if it was designed today, I bet it
>> would look quite different from what it is now.
>>
>>>
>>> 4. this api can be considered as extended 'blit' operation, other DRM
>>> drivers
>>>    (MGA, R128, VIA) already have ioctls for such operation, so there is also
>>>    place in DRM for it
> 
> Note that I am convince that using these custom IOCTL within a
> "compositor" implementation is much easier and uniform compared to
> using a v4l2 driver. It probably offers lower latency. But these are
> non-generic and are not a great fit for streaming purpose. Request API
> and probably explicit fence may mitigate this though. Meanwhile, there
> is some indication that even though complex, there is already some
> people that do think implementing a compositor combining V4L2 and DRM
> is feasible.
> 
> http://events.linuxfoundation.org/sites/events/files/slides/als2015_way
> land_weston_v2.pdf
> 
>>
>> Added LMML to cc.
> 
> Thanks.
> 

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Nicolas Dufresne]

[-- Attachment #1: Type: text/plain, Size: 12197 bytes --]

Le mercredi 26 avril 2017 à 18:52 +0200, Tobias Jakobi a écrit :
> Hello again,
> 
> 
> Nicolas Dufresne wrote:
> > Le mercredi 26 avril 2017 à 01:21 +0300, Sakari Ailus a écrit :
> > > Hi Marek,
> > > 
> > > On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
> > > > Hi Laurent,
> > > > 
> > > > On 2017-04-20 12:25, Laurent Pinchart wrote:
> > > > > Hi Marek,
> > > > > 
> > > > > (CC'ing Sakari Ailus)
> > > > > 
> > > > > Thank you for the patches.
> > > > > 
> > > > > On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
> > > > > > Dear all,
> > > > > > 
> > > > > > This is an updated proposal for extending EXYNOS DRM API with generic
> > > > > > support for hardware modules, which can be used for processing image data
> > > > > > from the one memory buffer to another. Typical memory-to-memory operations
> > > > > > are: rotation, scaling, colour space conversion or mix of them. This is a
> > > > > > follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
> > > > > > processors", which has been rejected as "not really needed in the DRM
> > > > > > core":
> > > > > > http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
> > > > > > 
> > > > > > In this proposal I moved all the code to Exynos DRM driver, so now this
> > > > > > will be specific only to Exynos DRM. I've also changed the name from
> > > > > > framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
> > > > > > with fbdev API.
> > > > > > 
> > > > > > Here is a bit more information what picture processors are:
> > > > > > 
> > > > > > Embedded SoCs are known to have a number of hardware blocks, which perform
> > > > > > such operations. They can be used in paralel to the main GPU module to
> > > > > > offload CPU from processing grapics or video data. One of example use of
> > > > > > such modules is implementing video overlay, which usually requires color
> > > > > > space conversion from NV12 (or similar) to RGB32 color space and scaling to
> > > > > > target window size.
> > > > > > 
> > > > > > The proposed API is heavily inspired by atomic KMS approach - it is also
> > > > > > based on DRM objects and their properties. A new DRM object is introduced:
> > > > > > picture processor (called pp for convenience). Such objects have a set of
> > > > > > standard DRM properties, which describes the operation to be performed by
> > > > > > respective hardware module. In typical case those properties are a source
> > > > > > fb id and rectangle (x, y, width, height) and destination fb id and
> > > > > > rectangle. Optionally a rotation property can be also specified if
> > > > > > supported by the given hardware. To perform an operation on image data,
> > > > > > userspace provides a set of properties and their values for given fbproc
> > > > > > object in a similar way as object and properties are provided for
> > > > > > performing atomic page flip / mode setting.
> > > > > > 
> > > > > > The proposed API consists of the 3 new ioctls:
> > > > > > - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
> > > > > >   processors,
> > > > > > - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
> > > > > >   processor,
> > > > > > - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
> > > > > >   property set.
> > > > > > 
> > > > > > The proposed API is extensible. Drivers can attach their own, custom
> > > > > > properties to add support for more advanced picture processing (for example
> > > > > > blending).
> > > > > > 
> > > > > > This proposal aims to replace Exynos DRM IPP (Image Post Processing)
> > > > > > subsystem. IPP API is over-engineered in general, but not really extensible
> > > > > > on the other side. It is also buggy, with significant design flaws - the
> > > > > > biggest issue is the fact that the API covers memory-2-memory picture
> > > > > > operations together with CRTC writeback and duplicating features, which
> > > > > > belongs to video plane. Comparing with IPP subsystem, the PP framework is
> > > > > > smaller (1807 vs 778 lines) and allows driver simplification (Exynos
> > > > > > rotator driver smaller by over 200 lines).
> > 
> > Just a side note, we have written code in GStreamer using the Exnynos 4
> > FIMC IPP driver. I don't know how many, if any, deployment still exist
> > (Exynos 4 is relatively old now), but there exist userspace for the
> > FIMC driver.
> 
> I was searching for this code, but I didn't find anything. Are you sure
> you really mean the FIMC IPP in Exynos DRM, and not just the FIMC driver
> from the V4L2 subsystem?

Oops, I manage to be unclear. Having two drivers on the same IP isn't
helping. We wrote code around the FIMC driver on V4L2 side. This
driver:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/media/platform/exynos4-is/fimc-m2m.c

And this code:

https://cgit.freedesktop.org/gstreamer/gst-plugins-good/tree/sys/v4l2/gstv4l2transform.c

Unless I have miss-read, the proposal here is to deprecate the V4L side
and improve the DRM side (which I stand against in my reply).

> 
> 
> With best wishes,
> Tobias
> 
> 
> 
> > We use this for color transformation (from tiled to
> > linear) and scaling. The FIMC driver is in fact quite stable in
> > upstream kernel today. The GScaler V4L2 M2M driver on Exynos 5 is
> > largely based on it and has received some maintenance to properly work
> > in GStreamer. unlike this DRM API, you can reuse the same userspace
> > code across multiple platforms (which we do already). We have also
> > integrated this driver in Chromium in the past (not upstream though).
> > 
> > I am well aware that the blitter driver has not got much attention
> > though. But again, V4L2 offers a generic interface to userspace
> > application. Fixing this driver could enable some work like this one:
> > 
> > https://bugzilla.gnome.org/show_bug.cgi?id=772766
> > 
> > This work in progress feature is a generic hardware accelerated video
> > mixer. It has been tested with IMX.6 v4l2 m2m blitter driver (which I
> > believe is in staging right now). Again, unlike the exynos/drm, this
> > code could be reused between platforms.
> > 
> > In general, the problem with the DRM approach is that it only targets
> > displays. We often need to use these IP block for stream pre/post
> > processing outside a "playback" use case.
> > 
> > What I'd like so see instead here, is an approach that helps both world
> >  instead of trying to win the control over the IP block. Renesas
> > development seems to lead toward the right direction by creating
> > drivers that can be both interfaced in DRM and V4L2. For IPP and
> > GScaler on Exynos, this would be a greater benefit and finally the code
> > could be shared, having a single place to fix when we find bugs.
> > 
> > > > > 
> > > > > This seems to be the kind of hardware that is typically supported by V4L2.
> > > > > Stupid question, why DRM ?
> > > > 
> > > > Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
> > > > 
> > > > 1. we want to replace existing Exynos IPP subsystem:
> > > >  - it is used only in some internal/vendor trees, not in open-source
> > > >  - we want it to have sane and potentially extensible userspace API
> > > >  - but we don't want to loose its functionality
> > > > 
> > > > 2. we want to have simple API for performing single image processing
> > > > operation:
> > > >  - typically it will be used by compositing window manager, this means that
> > > >    some parameters of the processing might change on each vblank (like
> > > >    destination rectangle for example). This api allows such change on each
> > > >    operation without any additional cost. V4L2 requires to reinitialize
> > > >    queues with new configuration on such change, what means that a bunch of
> > > >    ioctls has to be called.
> > > 
> > > What do you mean by re-initialising the queue? Format, buffers or something
> > > else?
> > > 
> > > If you need a larger buffer than what you have already allocated, you'll
> > > need to re-allocate, V4L2 or not.
> > > 
> > > We also do lack a way to destroy individual buffers in V4L2. It'd be up to
> > > implementing that and some work in videobuf2.
> > > 
> > > Another thing is that V4L2 is very stream oriented. For most devices that's
> > > fine as a lot of the parameters are not changeable during streaming,
> > > especially if the pipeline is handled by multiple drivers. That said, for
> > > devices that process data from memory to memory performing changes in the
> > > media bus formats and pipeline configuration is not very efficient
> > > currently, largely for the same reason.
> > > 
> > > The request API that people have been working for a bit different use cases
> > > isn't in mainline yet. It would allow more efficient per-request
> > > configuration than what is currently possible, but it has turned out to be
> > > far from trivial to implement.
> > > 
> > > >  - validating processing parameters in V4l2 API is really complicated,
> > > >    because the parameters (format, src&dest rectangles, rotation) are being
> > > >    set incrementally, so we have to either allow some impossible,
> > > > transitional
> > > >    configurations or complicate the configuration steps even more (like
> > > >    calling some ioctls multiple times for both input and output). In the end
> > > >    all parameters have to be again validated just before performing the
> > > >    operation.
> > > 
> > > You have to validate the parameters in any case. In a MC pipeline this takes
> > > place when the stream is started.
> > > 
> > > > 
> > > > 3. generic approach (to add it to DRM core) has been rejected:
> > > > http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
> > > 
> > > For GPUs I generally understand the reasoning: there's a very limited number
> > > of users of this API --- primarily because it's not an application
> > > interface.
> > > 
> > > If you have a device that however falls under the scope of V4L2 (at least
> > > API-wise), does this continue to be the case? Will there be only one or two
> > > (or so) users for this API? Is it the case here?
> > > 
> > > Using a device specific interface definitely has some benefits: there's no
> > > need to think how would you generalise the interface for other similar
> > > devices. There's no need to consider backwards compatibility as it's not a
> > > requirement. The drawback is that the applications that need to support
> > > similar devices will bear the burden of having to support different APIs.
> > > 
> > > I don't mean to say that you should ram whatever under V4L2 / MC
> > > independently of how unworkable that might be, but there are also clear
> > > advantages in using a standardised interface such as V4L2.
> > > 
> > > V4L2 has a long history behind it and if it was designed today, I bet it
> > > would look quite different from what it is now.
> > > 
> > > > 
> > > > 4. this api can be considered as extended 'blit' operation, other DRM
> > > > drivers
> > > >    (MGA, R128, VIA) already have ioctls for such operation, so there is also
> > > >    place in DRM for it
> > 
> > Note that I am convince that using these custom IOCTL within a
> > "compositor" implementation is much easier and uniform compared to
> > using a v4l2 driver. It probably offers lower latency. But these are
> > non-generic and are not a great fit for streaming purpose. Request API
> > and probably explicit fence may mitigate this though. Meanwhile, there
> > is some indication that even though complex, there is already some
> > people that do think implementing a compositor combining V4L2 and DRM
> > is feasible.
> > 
> > http://events.linuxfoundation.org/sites/events/files/slides/als2015_way
> > land_weston_v2.pdf
> > 
> > > 
> > > Added LMML to cc.
> > 
> > Thanks.
> > 
> 
> 

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Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Tobias Jakobi]

Hey,

Nicolas Dufresne wrote:
> Le mercredi 26 avril 2017 à 18:52 +0200, Tobias Jakobi a écrit :
>> Hello again,
>>
>>
>> Nicolas Dufresne wrote:
>>> Le mercredi 26 avril 2017 à 01:21 +0300, Sakari Ailus a écrit :
>>>> Hi Marek,
>>>>
>>>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>>>>> Hi Laurent,
>>>>>
>>>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>>>>> Hi Marek,
>>>>>>
>>>>>> (CC'ing Sakari Ailus)
>>>>>>
>>>>>> Thank you for the patches.
>>>>>>
>>>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>>>>> Dear all,
>>>>>>>
>>>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>>>>> support for hardware modules, which can be used for processing image data
>>>>>>> from the one memory buffer to another. Typical memory-to-memory operations
>>>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>>>>> processors", which has been rejected as "not really needed in the DRM
>>>>>>> core":
>>>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>>>
>>>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>>>>> with fbdev API.
>>>>>>>
>>>>>>> Here is a bit more information what picture processors are:
>>>>>>>
>>>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>>>>> such operations. They can be used in paralel to the main GPU module to
>>>>>>> offload CPU from processing grapics or video data. One of example use of
>>>>>>> such modules is implementing video overlay, which usually requires color
>>>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>>>>> target window size.
>>>>>>>
>>>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>>>>> picture processor (called pp for convenience). Such objects have a set of
>>>>>>> standard DRM properties, which describes the operation to be performed by
>>>>>>> respective hardware module. In typical case those properties are a source
>>>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>>>>> rectangle. Optionally a rotation property can be also specified if
>>>>>>> supported by the given hardware. To perform an operation on image data,
>>>>>>> userspace provides a set of properties and their values for given fbproc
>>>>>>> object in a similar way as object and properties are provided for
>>>>>>> performing atomic page flip / mode setting.
>>>>>>>
>>>>>>> The proposed API consists of the 3 new ioctls:
>>>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>>>>   processors,
>>>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>>>>   processor,
>>>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>>>>   property set.
>>>>>>>
>>>>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>>>>> properties to add support for more advanced picture processing (for example
>>>>>>> blending).
>>>>>>>
>>>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>>>>> on the other side. It is also buggy, with significant design flaws - the
>>>>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>>>>> operations together with CRTC writeback and duplicating features, which
>>>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>>>>> rotator driver smaller by over 200 lines).
>>>
>>> Just a side note, we have written code in GStreamer using the Exnynos 4
>>> FIMC IPP driver. I don't know how many, if any, deployment still exist
>>> (Exynos 4 is relatively old now), but there exist userspace for the
>>> FIMC driver.
>>
>> I was searching for this code, but I didn't find anything. Are you sure
>> you really mean the FIMC IPP in Exynos DRM, and not just the FIMC driver
>> from the V4L2 subsystem?
> 
> Oops, I manage to be unclear. Having two drivers on the same IP isn't
> helping. We wrote code around the FIMC driver on V4L2 side. This
> driver:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/media/platform/exynos4-is/fimc-m2m.c
> 
> And this code:
> 
> https://cgit.freedesktop.org/gstreamer/gst-plugins-good/tree/sys/v4l2/gstv4l2transform.c
> 
> Unless I have miss-read, the proposal here is to deprecate the V4L side
> and improve the DRM side (which I stand against in my reply).
I'm pretty sure you have misread Marek's description of the patchset.
The picture processor API should replaced/deprecate the IPP API that is
currently implemented in the Exynos DRM.

In particular this affects the following files:
- drivers/gpu/drm/exynos/exynos_drm_ipp.{c,h}
- drivers/gpu/drm/exynos/exynos_drm_fimc.{c,h}
- drivers/gpu/drm/exynos/exynos_drm_gsc.{c,h}
- drivers/gpu/drm/exynos/exynos_drm_rotator.{c,h}

I know only two places where the IPP API is actually used. Tizen and my
experimental mpv backend.

With best wishes,
Tobias



> 
>>
>>
>> With best wishes,
>> Tobias
>>
>>
>>
>>> We use this for color transformation (from tiled to
>>> linear) and scaling. The FIMC driver is in fact quite stable in
>>> upstream kernel today. The GScaler V4L2 M2M driver on Exynos 5 is
>>> largely based on it and has received some maintenance to properly work
>>> in GStreamer. unlike this DRM API, you can reuse the same userspace
>>> code across multiple platforms (which we do already). We have also
>>> integrated this driver in Chromium in the past (not upstream though).
>>>
>>> I am well aware that the blitter driver has not got much attention
>>> though. But again, V4L2 offers a generic interface to userspace
>>> application. Fixing this driver could enable some work like this one:
>>>
>>> https://bugzilla.gnome.org/show_bug.cgi?id=772766
>>>
>>> This work in progress feature is a generic hardware accelerated video
>>> mixer. It has been tested with IMX.6 v4l2 m2m blitter driver (which I
>>> believe is in staging right now). Again, unlike the exynos/drm, this
>>> code could be reused between platforms.
>>>
>>> In general, the problem with the DRM approach is that it only targets
>>> displays. We often need to use these IP block for stream pre/post
>>> processing outside a "playback" use case.
>>>
>>> What I'd like so see instead here, is an approach that helps both world
>>>  instead of trying to win the control over the IP block. Renesas
>>> development seems to lead toward the right direction by creating
>>> drivers that can be both interfaced in DRM and V4L2. For IPP and
>>> GScaler on Exynos, this would be a greater benefit and finally the code
>>> could be shared, having a single place to fix when we find bugs.
>>>
>>>>>>
>>>>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>>>>> Stupid question, why DRM ?
>>>>>
>>>>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>>>>
>>>>> 1. we want to replace existing Exynos IPP subsystem:
>>>>>  - it is used only in some internal/vendor trees, not in open-source
>>>>>  - we want it to have sane and potentially extensible userspace API
>>>>>  - but we don't want to loose its functionality
>>>>>
>>>>> 2. we want to have simple API for performing single image processing
>>>>> operation:
>>>>>  - typically it will be used by compositing window manager, this means that
>>>>>    some parameters of the processing might change on each vblank (like
>>>>>    destination rectangle for example). This api allows such change on each
>>>>>    operation without any additional cost. V4L2 requires to reinitialize
>>>>>    queues with new configuration on such change, what means that a bunch of
>>>>>    ioctls has to be called.
>>>>
>>>> What do you mean by re-initialising the queue? Format, buffers or something
>>>> else?
>>>>
>>>> If you need a larger buffer than what you have already allocated, you'll
>>>> need to re-allocate, V4L2 or not.
>>>>
>>>> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
>>>> implementing that and some work in videobuf2.
>>>>
>>>> Another thing is that V4L2 is very stream oriented. For most devices that's
>>>> fine as a lot of the parameters are not changeable during streaming,
>>>> especially if the pipeline is handled by multiple drivers. That said, for
>>>> devices that process data from memory to memory performing changes in the
>>>> media bus formats and pipeline configuration is not very efficient
>>>> currently, largely for the same reason.
>>>>
>>>> The request API that people have been working for a bit different use cases
>>>> isn't in mainline yet. It would allow more efficient per-request
>>>> configuration than what is currently possible, but it has turned out to be
>>>> far from trivial to implement.
>>>>
>>>>>  - validating processing parameters in V4l2 API is really complicated,
>>>>>    because the parameters (format, src&dest rectangles, rotation) are being
>>>>>    set incrementally, so we have to either allow some impossible,
>>>>> transitional
>>>>>    configurations or complicate the configuration steps even more (like
>>>>>    calling some ioctls multiple times for both input and output). In the end
>>>>>    all parameters have to be again validated just before performing the
>>>>>    operation.
>>>>
>>>> You have to validate the parameters in any case. In a MC pipeline this takes
>>>> place when the stream is started.
>>>>
>>>>>
>>>>> 3. generic approach (to add it to DRM core) has been rejected:
>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>
>>>> For GPUs I generally understand the reasoning: there's a very limited number
>>>> of users of this API --- primarily because it's not an application
>>>> interface.
>>>>
>>>> If you have a device that however falls under the scope of V4L2 (at least
>>>> API-wise), does this continue to be the case? Will there be only one or two
>>>> (or so) users for this API? Is it the case here?
>>>>
>>>> Using a device specific interface definitely has some benefits: there's no
>>>> need to think how would you generalise the interface for other similar
>>>> devices. There's no need to consider backwards compatibility as it's not a
>>>> requirement. The drawback is that the applications that need to support
>>>> similar devices will bear the burden of having to support different APIs.
>>>>
>>>> I don't mean to say that you should ram whatever under V4L2 / MC
>>>> independently of how unworkable that might be, but there are also clear
>>>> advantages in using a standardised interface such as V4L2.
>>>>
>>>> V4L2 has a long history behind it and if it was designed today, I bet it
>>>> would look quite different from what it is now.
>>>>
>>>>>
>>>>> 4. this api can be considered as extended 'blit' operation, other DRM
>>>>> drivers
>>>>>    (MGA, R128, VIA) already have ioctls for such operation, so there is also
>>>>>    place in DRM for it
>>>
>>> Note that I am convince that using these custom IOCTL within a
>>> "compositor" implementation is much easier and uniform compared to
>>> using a v4l2 driver. It probably offers lower latency. But these are
>>> non-generic and are not a great fit for streaming purpose. Request API
>>> and probably explicit fence may mitigate this though. Meanwhile, there
>>> is some indication that even though complex, there is already some
>>> people that do think implementing a compositor combining V4L2 and DRM
>>> is feasible.
>>>
>>> http://events.linuxfoundation.org/sites/events/files/slides/als2015_way
>>> land_weston_v2.pdf
>>>
>>>>
>>>> Added LMML to cc.
>>>
>>> Thanks.
>>>
>>

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Nicolas Dufresne]

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Le mercredi 26 avril 2017 à 21:31 +0200, Tobias Jakobi a écrit :
> I'm pretty sure you have misread Marek's description of the patchset.
> The picture processor API should replaced/deprecate the IPP API that is
> currently implemented in the Exynos DRM.
> 
> In particular this affects the following files:
> - drivers/gpu/drm/exynos/exynos_drm_ipp.{c,h}
> - drivers/gpu/drm/exynos/exynos_drm_fimc.{c,h}
> - drivers/gpu/drm/exynos/exynos_drm_gsc.{c,h}
> - drivers/gpu/drm/exynos/exynos_drm_rotator.{c,h}
> 
> I know only two places where the IPP API is actually used. Tizen and my
> experimental mpv backend.

Sorry for the noise then.

regards,
Nicolas

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Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Marek Szyprowski]

Hi Sakari,

On 2017-04-26 00:21, Sakari Ailus wrote:
> Hi Marek,
>
> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>> Hi Laurent,
>>
>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>> Hi Marek,
>>>
>>> (CC'ing Sakari Ailus)
>>>
>>> Thank you for the patches.
>>>
>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>> Dear all,
>>>>
>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>> support for hardware modules, which can be used for processing image data
>>> >from the one memory buffer to another. Typical memory-to-memory operations
>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>> processors", which has been rejected as "not really needed in the DRM
>>>> core":
>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>
>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>> with fbdev API.
>>>>
>>>> Here is a bit more information what picture processors are:
>>>>
>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>> such operations. They can be used in paralel to the main GPU module to
>>>> offload CPU from processing grapics or video data. One of example use of
>>>> such modules is implementing video overlay, which usually requires color
>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>> target window size.
>>>>
>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>> picture processor (called pp for convenience). Such objects have a set of
>>>> standard DRM properties, which describes the operation to be performed by
>>>> respective hardware module. In typical case those properties are a source
>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>> rectangle. Optionally a rotation property can be also specified if
>>>> supported by the given hardware. To perform an operation on image data,
>>>> userspace provides a set of properties and their values for given fbproc
>>>> object in a similar way as object and properties are provided for
>>>> performing atomic page flip / mode setting.
>>>>
>>>> The proposed API consists of the 3 new ioctls:
>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>    processors,
>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>    processor,
>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>    property set.
>>>>
>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>> properties to add support for more advanced picture processing (for example
>>>> blending).
>>>>
>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>> on the other side. It is also buggy, with significant design flaws - the
>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>> operations together with CRTC writeback and duplicating features, which
>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>> rotator driver smaller by over 200 lines).
>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>> Stupid question, why DRM ?
>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>
>> 1. we want to replace existing Exynos IPP subsystem:
>>   - it is used only in some internal/vendor trees, not in open-source
>>   - we want it to have sane and potentially extensible userspace API
>>   - but we don't want to loose its functionality
>>
>> 2. we want to have simple API for performing single image processing
>> operation:
>>   - typically it will be used by compositing window manager, this means that
>>     some parameters of the processing might change on each vblank (like
>>     destination rectangle for example). This api allows such change on each
>>     operation without any additional cost. V4L2 requires to reinitialize
>>     queues with new configuration on such change, what means that a bunch of
>>     ioctls has to be called.
> What do you mean by re-initialising the queue? Format, buffers or something
> else?

In case of compositor use case, the parameter that is being changed most
frequently is source and/or destination rectangle position and/or size.

> If you need a larger buffer than what you have already allocated, you'll
> need to re-allocate, V4L2 or not.
>
> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
> implementing that and some work in videobuf2.

Well if we would use V4l2, buffers will always come as dmabuf objects. There
is a hard limit of the number of buffers that can be imported to v4l2/vb2
queue to get buffer ids. This also limits easy processing of the buffers
in the compositor, because you would need to reinitialize the v4l2 queues
to get new set of v4l2/vb2 buffer ids.

> Another thing is that V4L2 is very stream oriented. For most devices that's
> fine as a lot of the parameters are not changeable during streaming,
> especially if the pipeline is handled by multiple drivers. That said, for
> devices that process data from memory to memory performing changes in the
> media bus formats and pipeline configuration is not very efficient
> currently, largely for the same reason.
>
> The request API that people have been working for a bit different use cases
> isn't in mainline yet. It would allow more efficient per-request
> configuration than what is currently possible, but it has turned out to be
> far from trivial to implement.
>
>>   - validating processing parameters in V4l2 API is really complicated,
>>     because the parameters (format, src&dest rectangles, rotation) are being
>>     set incrementally, so we have to either allow some impossible,
>> transitional
>>     configurations or complicate the configuration steps even more (like
>>     calling some ioctls multiple times for both input and output). In the end
>>     all parameters have to be again validated just before performing the
>>     operation.
> You have to validate the parameters in any case. In a MC pipeline this takes
> place when the stream is started.

Well, in case of v4l2 one would need to stop and restart 'steaming' on 
both queues
of mem2mem device just to change some transformation parameters...

>> 3. generic approach (to add it to DRM core) has been rejected:
>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
> For GPUs I generally understand the reasoning: there's a very limited number
> of users of this API --- primarily because it's not an application
> interface.
>
> If you have a device that however falls under the scope of V4L2 (at least
> API-wise), does this continue to be the case? Will there be only one or two
> (or so) users for this API? Is it the case here?
>
> Using a device specific interface definitely has some benefits: there's no
> need to think how would you generalise the interface for other similar
> devices. There's no need to consider backwards compatibility as it's not a
> requirement. The drawback is that the applications that need to support
> similar devices will bear the burden of having to support different APIs.
>
> I don't mean to say that you should ram whatever under V4L2 / MC
> independently of how unworkable that might be, but there are also clear
> advantages in using a standardised interface such as V4L2.
>
> V4L2 has a long history behind it and if it was designed today, I bet it
> would look quite different from what it is now.

IMHO V4l2 becomes both a bit over-engineered because of the 'backwards
compatibility' and too limited on the other hand to support really complex
hardware (iirc none of the top mobile Android HW vendors use V4l2 for their
cameras subsystems). This is however a completely separate topic.

>> 4. this api can be considered as extended 'blit' operation, other DRM
>> drivers
>>     (MGA, R128, VIA) already have ioctls for such operation, so there is also
>>     place in DRM for it
> Added LMML to cc.
>

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Inki Dae]

2017년 04월 26일 07:21에 Sakari Ailus 이(가) 쓴 글:
> Hi Marek,
> 
> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>> Hi Laurent,
>>
>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>> Hi Marek,
>>>
>>> (CC'ing Sakari Ailus)
>>>
>>> Thank you for the patches.
>>>
>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>> Dear all,
>>>>
>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>> support for hardware modules, which can be used for processing image data
>>> >from the one memory buffer to another. Typical memory-to-memory operations
>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>> processors", which has been rejected as "not really needed in the DRM
>>>> core":
>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>
>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>> with fbdev API.
>>>>
>>>> Here is a bit more information what picture processors are:
>>>>
>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>> such operations. They can be used in paralel to the main GPU module to
>>>> offload CPU from processing grapics or video data. One of example use of
>>>> such modules is implementing video overlay, which usually requires color
>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>> target window size.
>>>>
>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>> picture processor (called pp for convenience). Such objects have a set of
>>>> standard DRM properties, which describes the operation to be performed by
>>>> respective hardware module. In typical case those properties are a source
>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>> rectangle. Optionally a rotation property can be also specified if
>>>> supported by the given hardware. To perform an operation on image data,
>>>> userspace provides a set of properties and their values for given fbproc
>>>> object in a similar way as object and properties are provided for
>>>> performing atomic page flip / mode setting.
>>>>
>>>> The proposed API consists of the 3 new ioctls:
>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>   processors,
>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>   processor,
>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>   property set.
>>>>
>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>> properties to add support for more advanced picture processing (for example
>>>> blending).
>>>>
>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>> on the other side. It is also buggy, with significant design flaws - the
>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>> operations together with CRTC writeback and duplicating features, which
>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>> rotator driver smaller by over 200 lines).
>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>> Stupid question, why DRM ?
>>
>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>
>> 1. we want to replace existing Exynos IPP subsystem:
>>  - it is used only in some internal/vendor trees, not in open-source
>>  - we want it to have sane and potentially extensible userspace API
>>  - but we don't want to loose its functionality
>>
>> 2. we want to have simple API for performing single image processing
>> operation:
>>  - typically it will be used by compositing window manager, this means that
>>    some parameters of the processing might change on each vblank (like
>>    destination rectangle for example). This api allows such change on each
>>    operation without any additional cost. V4L2 requires to reinitialize
>>    queues with new configuration on such change, what means that a bunch of
>>    ioctls has to be called.
> 
> What do you mean by re-initialising the queue? Format, buffers or something
> else?
> 
> If you need a larger buffer than what you have already allocated, you'll
> need to re-allocate, V4L2 or not.
> 
> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
> implementing that and some work in videobuf2.
> 
> Another thing is that V4L2 is very stream oriented. For most devices that's
> fine as a lot of the parameters are not changeable during streaming,
> especially if the pipeline is handled by multiple drivers. That said, for
> devices that process data from memory to memory performing changes in the
> media bus formats and pipeline configuration is not very efficient
> currently, largely for the same reason.
> 
> The request API that people have been working for a bit different use cases
> isn't in mainline yet. It would allow more efficient per-request
> configuration than what is currently possible, but it has turned out to be
> far from trivial to implement.
> 
>>  - validating processing parameters in V4l2 API is really complicated,
>>    because the parameters (format, src&dest rectangles, rotation) are being
>>    set incrementally, so we have to either allow some impossible,
>> transitional
>>    configurations or complicate the configuration steps even more (like
>>    calling some ioctls multiple times for both input and output). In the end
>>    all parameters have to be again validated just before performing the
>>    operation.
> 
> You have to validate the parameters in any case. In a MC pipeline this takes
> place when the stream is started.
> 
>>
>> 3. generic approach (to add it to DRM core) has been rejected:
>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
> 
> For GPUs I generally understand the reasoning: there's a very limited number
> of users of this API --- primarily because it's not an application
> interface.
> 
> If you have a device that however falls under the scope of V4L2 (at least
> API-wise), does this continue to be the case? Will there be only one or two
> (or so) users for this API? Is it the case here?
> 
> Using a device specific interface definitely has some benefits: there's no
> need to think how would you generalise the interface for other similar
> devices. There's no need to consider backwards compatibility as it's not a
> requirement. The drawback is that the applications that need to support
> similar devices will bear the burden of having to support different APIs.
> 
> I don't mean to say that you should ram whatever under V4L2 / MC
> independently of how unworkable that might be, but there are also clear
> advantages in using a standardised interface such as V4L2.
> 
> V4L2 has a long history behind it and if it was designed today, I bet it
> would look quite different from what it is now.

It's true. There is definitely a benefit with V4L2 because V4L2 provides Linux standard ABI - for DRM as of now not.

However, I think that is a only benefit we could get through V4L2. Using V4L2 makes software stack of Platform to be complicated - We have to open video device node and card device node to display a image on the screen scaling or converting color space of the image and also we need to export DMA buffer from one side and import it to other side using DMABUF.

It may not related to this but even V4L2 has performance problem - every QBUF/DQBUF requests performs mapping/unmapping DMA buffer you already know this. :)

In addition, recently Display subsystems on ARM SoC tend to include pre/post processing hardware in Display controller - OMAP, Exynos8895 and MSM as long as I know.


Thanks,
Inki Dae

> 
>>
>> 4. this api can be considered as extended 'blit' operation, other DRM
>> drivers
>>    (MGA, R128, VIA) already have ioctls for such operation, so there is also
>>    place in DRM for it
> 
> Added LMML to cc.
> 

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Tomasz Figa]

Hi Everyone,

On Wed, May 10, 2017 at 9:24 AM, Inki Dae <inki.dae@samsung.com> wrote:
>
>
> 2017년 04월 26일 07:21에 Sakari Ailus 이(가) 쓴 글:
>> Hi Marek,
>>
>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>>> Hi Laurent,
>>>
>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>>> Hi Marek,
>>>>
>>>> (CC'ing Sakari Ailus)
>>>>
>>>> Thank you for the patches.
>>>>
>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>>> Dear all,
>>>>>
>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>>> support for hardware modules, which can be used for processing image data
>>>> >from the one memory buffer to another. Typical memory-to-memory operations
>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>>> processors", which has been rejected as "not really needed in the DRM
>>>>> core":
>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>
>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>>> with fbdev API.
>>>>>
>>>>> Here is a bit more information what picture processors are:
>>>>>
>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>>> such operations. They can be used in paralel to the main GPU module to
>>>>> offload CPU from processing grapics or video data. One of example use of
>>>>> such modules is implementing video overlay, which usually requires color
>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>>> target window size.
>>>>>
>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>>> picture processor (called pp for convenience). Such objects have a set of
>>>>> standard DRM properties, which describes the operation to be performed by
>>>>> respective hardware module. In typical case those properties are a source
>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>>> rectangle. Optionally a rotation property can be also specified if
>>>>> supported by the given hardware. To perform an operation on image data,
>>>>> userspace provides a set of properties and their values for given fbproc
>>>>> object in a similar way as object and properties are provided for
>>>>> performing atomic page flip / mode setting.
>>>>>
>>>>> The proposed API consists of the 3 new ioctls:
>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>>   processors,
>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>>   processor,
>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>>   property set.
>>>>>
>>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>>> properties to add support for more advanced picture processing (for example
>>>>> blending).
>>>>>
>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>>> on the other side. It is also buggy, with significant design flaws - the
>>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>>> operations together with CRTC writeback and duplicating features, which
>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>>> rotator driver smaller by over 200 lines).
>>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>>> Stupid question, why DRM ?
>>>
>>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>>
>>> 1. we want to replace existing Exynos IPP subsystem:
>>>  - it is used only in some internal/vendor trees, not in open-source
>>>  - we want it to have sane and potentially extensible userspace API
>>>  - but we don't want to loose its functionality
>>>
>>> 2. we want to have simple API for performing single image processing
>>> operation:
>>>  - typically it will be used by compositing window manager, this means that
>>>    some parameters of the processing might change on each vblank (like
>>>    destination rectangle for example). This api allows such change on each
>>>    operation without any additional cost. V4L2 requires to reinitialize
>>>    queues with new configuration on such change, what means that a bunch of
>>>    ioctls has to be called.
>>
>> What do you mean by re-initialising the queue? Format, buffers or something
>> else?
>>
>> If you need a larger buffer than what you have already allocated, you'll
>> need to re-allocate, V4L2 or not.
>>
>> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
>> implementing that and some work in videobuf2.
>>
>> Another thing is that V4L2 is very stream oriented. For most devices that's
>> fine as a lot of the parameters are not changeable during streaming,
>> especially if the pipeline is handled by multiple drivers. That said, for
>> devices that process data from memory to memory performing changes in the
>> media bus formats and pipeline configuration is not very efficient
>> currently, largely for the same reason.
>>
>> The request API that people have been working for a bit different use cases
>> isn't in mainline yet. It would allow more efficient per-request
>> configuration than what is currently possible, but it has turned out to be
>> far from trivial to implement.
>>
>>>  - validating processing parameters in V4l2 API is really complicated,
>>>    because the parameters (format, src&dest rectangles, rotation) are being
>>>    set incrementally, so we have to either allow some impossible,
>>> transitional
>>>    configurations or complicate the configuration steps even more (like
>>>    calling some ioctls multiple times for both input and output). In the end
>>>    all parameters have to be again validated just before performing the
>>>    operation.
>>
>> You have to validate the parameters in any case. In a MC pipeline this takes
>> place when the stream is started.
>>
>>>
>>> 3. generic approach (to add it to DRM core) has been rejected:
>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>
>> For GPUs I generally understand the reasoning: there's a very limited number
>> of users of this API --- primarily because it's not an application
>> interface.
>>
>> If you have a device that however falls under the scope of V4L2 (at least
>> API-wise), does this continue to be the case? Will there be only one or two
>> (or so) users for this API? Is it the case here?
>>
>> Using a device specific interface definitely has some benefits: there's no
>> need to think how would you generalise the interface for other similar
>> devices. There's no need to consider backwards compatibility as it's not a
>> requirement. The drawback is that the applications that need to support
>> similar devices will bear the burden of having to support different APIs.
>>
>> I don't mean to say that you should ram whatever under V4L2 / MC
>> independently of how unworkable that might be, but there are also clear
>> advantages in using a standardised interface such as V4L2.
>>
>> V4L2 has a long history behind it and if it was designed today, I bet it
>> would look quite different from what it is now.
>
> It's true. There is definitely a benefit with V4L2 because V4L2 provides Linux standard ABI - for DRM as of now not.
>
> However, I think that is a only benefit we could get through V4L2. Using V4L2 makes software stack of Platform to be complicated - We have to open video device node and card device node to display a image on the screen scaling or converting color space of the image and also we need to export DMA buffer from one side and import it to other side using DMABUF.
>
> It may not related to this but even V4L2 has performance problem - every QBUF/DQBUF requests performs mapping/unmapping DMA buffer you already know this. :)
>
> In addition, recently Display subsystems on ARM SoC tend to include pre/post processing hardware in Display controller - OMAP, Exynos8895 and MSM as long as I know.
>

I agree with many of the arguments given by Inki above and earlier by
Marek. However, they apply to already existing V4L2 implementation,
not V4L2 as the idea in general, and I believe a comparison against a
complete new API that doesn't even exist in the kernel tree and
userspace yet (only in terms of patches on the list) is not fair.

I strongly (if that's of any value) stand on Sakari's side and also
agree with DRM maintainers. V4L2 is already there, provides a general
interface for the userspace and already support the kind of devices
Marek mention. Sure, it might have several issues, but please give me
an example of a subsystem/interface/code that doesn't have any.
Instead of taking the easy (for short term) path, with a bit more
effort we can get something than in long run should end up much
better.

Best regards,
Tomasz

>
> Thanks,
> Inki Dae
>
>>
>>>
>>> 4. this api can be considered as extended 'blit' operation, other DRM
>>> drivers
>>>    (MGA, R128, VIA) already have ioctls for such operation, so there is also
>>>    place in DRM for it
>>
>> Added LMML to cc.
>>

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Inki Dae]

Hi Tomasz,

2017년 05월 10일 14:38에 Tomasz Figa 이(가) 쓴 글:
> Hi Everyone,
> 
> On Wed, May 10, 2017 at 9:24 AM, Inki Dae <inki.dae@samsung.com> wrote:
>>
>>
>> 2017년 04월 26일 07:21에 Sakari Ailus 이(가) 쓴 글:
>>> Hi Marek,
>>>
>>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>>>> Hi Laurent,
>>>>
>>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>>>> Hi Marek,
>>>>>
>>>>> (CC'ing Sakari Ailus)
>>>>>
>>>>> Thank you for the patches.
>>>>>
>>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>>>> Dear all,
>>>>>>
>>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>>>> support for hardware modules, which can be used for processing image data
>>>>> >from the one memory buffer to another. Typical memory-to-memory operations
>>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>>>> processors", which has been rejected as "not really needed in the DRM
>>>>>> core":
>>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>>
>>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>>>> with fbdev API.
>>>>>>
>>>>>> Here is a bit more information what picture processors are:
>>>>>>
>>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>>>> such operations. They can be used in paralel to the main GPU module to
>>>>>> offload CPU from processing grapics or video data. One of example use of
>>>>>> such modules is implementing video overlay, which usually requires color
>>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>>>> target window size.
>>>>>>
>>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>>>> picture processor (called pp for convenience). Such objects have a set of
>>>>>> standard DRM properties, which describes the operation to be performed by
>>>>>> respective hardware module. In typical case those properties are a source
>>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>>>> rectangle. Optionally a rotation property can be also specified if
>>>>>> supported by the given hardware. To perform an operation on image data,
>>>>>> userspace provides a set of properties and their values for given fbproc
>>>>>> object in a similar way as object and properties are provided for
>>>>>> performing atomic page flip / mode setting.
>>>>>>
>>>>>> The proposed API consists of the 3 new ioctls:
>>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>>>   processors,
>>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>>>   processor,
>>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>>>   property set.
>>>>>>
>>>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>>>> properties to add support for more advanced picture processing (for example
>>>>>> blending).
>>>>>>
>>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>>>> on the other side. It is also buggy, with significant design flaws - the
>>>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>>>> operations together with CRTC writeback and duplicating features, which
>>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>>>> rotator driver smaller by over 200 lines).
>>>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>>>> Stupid question, why DRM ?
>>>>
>>>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>>>
>>>> 1. we want to replace existing Exynos IPP subsystem:
>>>>  - it is used only in some internal/vendor trees, not in open-source
>>>>  - we want it to have sane and potentially extensible userspace API
>>>>  - but we don't want to loose its functionality
>>>>
>>>> 2. we want to have simple API for performing single image processing
>>>> operation:
>>>>  - typically it will be used by compositing window manager, this means that
>>>>    some parameters of the processing might change on each vblank (like
>>>>    destination rectangle for example). This api allows such change on each
>>>>    operation without any additional cost. V4L2 requires to reinitialize
>>>>    queues with new configuration on such change, what means that a bunch of
>>>>    ioctls has to be called.
>>>
>>> What do you mean by re-initialising the queue? Format, buffers or something
>>> else?
>>>
>>> If you need a larger buffer than what you have already allocated, you'll
>>> need to re-allocate, V4L2 or not.
>>>
>>> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
>>> implementing that and some work in videobuf2.
>>>
>>> Another thing is that V4L2 is very stream oriented. For most devices that's
>>> fine as a lot of the parameters are not changeable during streaming,
>>> especially if the pipeline is handled by multiple drivers. That said, for
>>> devices that process data from memory to memory performing changes in the
>>> media bus formats and pipeline configuration is not very efficient
>>> currently, largely for the same reason.
>>>
>>> The request API that people have been working for a bit different use cases
>>> isn't in mainline yet. It would allow more efficient per-request
>>> configuration than what is currently possible, but it has turned out to be
>>> far from trivial to implement.
>>>
>>>>  - validating processing parameters in V4l2 API is really complicated,
>>>>    because the parameters (format, src&dest rectangles, rotation) are being
>>>>    set incrementally, so we have to either allow some impossible,
>>>> transitional
>>>>    configurations or complicate the configuration steps even more (like
>>>>    calling some ioctls multiple times for both input and output). In the end
>>>>    all parameters have to be again validated just before performing the
>>>>    operation.
>>>
>>> You have to validate the parameters in any case. In a MC pipeline this takes
>>> place when the stream is started.
>>>
>>>>
>>>> 3. generic approach (to add it to DRM core) has been rejected:
>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>
>>> For GPUs I generally understand the reasoning: there's a very limited number
>>> of users of this API --- primarily because it's not an application
>>> interface.
>>>
>>> If you have a device that however falls under the scope of V4L2 (at least
>>> API-wise), does this continue to be the case? Will there be only one or two
>>> (or so) users for this API? Is it the case here?
>>>
>>> Using a device specific interface definitely has some benefits: there's no
>>> need to think how would you generalise the interface for other similar
>>> devices. There's no need to consider backwards compatibility as it's not a
>>> requirement. The drawback is that the applications that need to support
>>> similar devices will bear the burden of having to support different APIs.
>>>
>>> I don't mean to say that you should ram whatever under V4L2 / MC
>>> independently of how unworkable that might be, but there are also clear
>>> advantages in using a standardised interface such as V4L2.
>>>
>>> V4L2 has a long history behind it and if it was designed today, I bet it
>>> would look quite different from what it is now.
>>
>> It's true. There is definitely a benefit with V4L2 because V4L2 provides Linux standard ABI - for DRM as of now not.
>>
>> However, I think that is a only benefit we could get through V4L2. Using V4L2 makes software stack of Platform to be complicated - We have to open video device node and card device node to display a image on the screen scaling or converting color space of the image and also we need to export DMA buffer from one side and import it to other side using DMABUF.
>>
>> It may not related to this but even V4L2 has performance problem - every QBUF/DQBUF requests performs mapping/unmapping DMA buffer you already know this. :)
>>
>> In addition, recently Display subsystems on ARM SoC tend to include pre/post processing hardware in Display controller - OMAP, Exynos8895 and MSM as long as I know.
>>
> 
> I agree with many of the arguments given by Inki above and earlier by
> Marek. However, they apply to already existing V4L2 implementation,
> not V4L2 as the idea in general, and I believe a comparison against a
> complete new API that doesn't even exist in the kernel tree and
> userspace yet (only in terms of patches on the list) is not fair.

Below is a user space who uses Exynos DRM post processor driver, IPP driver.
https://review.tizen.org/git/?p=platform/adaptation/samsung_exynos/libtdm-exynos.git;a=blob;f=src/tdm_exynos_pp.c;h=db20e6f226d313672d1d468e06d80526ea30121c;hb=refs/heads/tizen

Marek patch series is just a new version of this driver which is specific to Exynos DRM. Marek is trying to enhance this driver.
Ps. other DRM drivers in mainline already have such or similar API.

We will also open the user space who uses new API later.


Thanks,
Inki Dae

> 
> I strongly (if that's of any value) stand on Sakari's side and also
> agree with DRM maintainers. V4L2 is already there, provides a general
> interface for the userspace and already support the kind of devices
> Marek mention. Sure, it might have several issues, but please give me
> an example of a subsystem/interface/code that doesn't have any.
> Instead of taking the easy (for short term) path, with a bit more
> effort we can get something than in long run should end up much
> better.
> 
> Best regards,
> Tomasz
> 
>>
>> Thanks,
>> Inki Dae
>>
>>>
>>>>
>>>> 4. this api can be considered as extended 'blit' operation, other DRM
>>>> drivers
>>>>    (MGA, R128, VIA) already have ioctls for such operation, so there is also
>>>>    place in DRM for it
>>>
>>> Added LMML to cc.
>>>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 
> 
> 

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Tomasz Figa]

On Wed, May 10, 2017 at 2:27 PM, Inki Dae <inki.dae@samsung.com> wrote:
> Hi Tomasz,
>
> 2017년 05월 10일 14:38에 Tomasz Figa 이(가) 쓴 글:
>> Hi Everyone,
>>
>> On Wed, May 10, 2017 at 9:24 AM, Inki Dae <inki.dae@samsung.com> wrote:
>>>
>>>
>>> 2017년 04월 26일 07:21에 Sakari Ailus 이(가) 쓴 글:
>>>> Hi Marek,
>>>>
>>>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>>>>> Hi Laurent,
>>>>>
>>>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>>>>> Hi Marek,
>>>>>>
>>>>>> (CC'ing Sakari Ailus)
>>>>>>
>>>>>> Thank you for the patches.
>>>>>>
>>>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>>>>> Dear all,
>>>>>>>
>>>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>>>>> support for hardware modules, which can be used for processing image data
>>>>>> >from the one memory buffer to another. Typical memory-to-memory operations
>>>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>>>>> processors", which has been rejected as "not really needed in the DRM
>>>>>>> core":
>>>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>>>
>>>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>>>>> with fbdev API.
>>>>>>>
>>>>>>> Here is a bit more information what picture processors are:
>>>>>>>
>>>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>>>>> such operations. They can be used in paralel to the main GPU module to
>>>>>>> offload CPU from processing grapics or video data. One of example use of
>>>>>>> such modules is implementing video overlay, which usually requires color
>>>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>>>>> target window size.
>>>>>>>
>>>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>>>>> picture processor (called pp for convenience). Such objects have a set of
>>>>>>> standard DRM properties, which describes the operation to be performed by
>>>>>>> respective hardware module. In typical case those properties are a source
>>>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>>>>> rectangle. Optionally a rotation property can be also specified if
>>>>>>> supported by the given hardware. To perform an operation on image data,
>>>>>>> userspace provides a set of properties and their values for given fbproc
>>>>>>> object in a similar way as object and properties are provided for
>>>>>>> performing atomic page flip / mode setting.
>>>>>>>
>>>>>>> The proposed API consists of the 3 new ioctls:
>>>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>>>>   processors,
>>>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>>>>   processor,
>>>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>>>>   property set.
>>>>>>>
>>>>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>>>>> properties to add support for more advanced picture processing (for example
>>>>>>> blending).
>>>>>>>
>>>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>>>>> on the other side. It is also buggy, with significant design flaws - the
>>>>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>>>>> operations together with CRTC writeback and duplicating features, which
>>>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>>>>> rotator driver smaller by over 200 lines).
>>>>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>>>>> Stupid question, why DRM ?
>>>>>
>>>>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>>>>
>>>>> 1. we want to replace existing Exynos IPP subsystem:
>>>>>  - it is used only in some internal/vendor trees, not in open-source
>>>>>  - we want it to have sane and potentially extensible userspace API
>>>>>  - but we don't want to loose its functionality
>>>>>
>>>>> 2. we want to have simple API for performing single image processing
>>>>> operation:
>>>>>  - typically it will be used by compositing window manager, this means that
>>>>>    some parameters of the processing might change on each vblank (like
>>>>>    destination rectangle for example). This api allows such change on each
>>>>>    operation without any additional cost. V4L2 requires to reinitialize
>>>>>    queues with new configuration on such change, what means that a bunch of
>>>>>    ioctls has to be called.
>>>>
>>>> What do you mean by re-initialising the queue? Format, buffers or something
>>>> else?
>>>>
>>>> If you need a larger buffer than what you have already allocated, you'll
>>>> need to re-allocate, V4L2 or not.
>>>>
>>>> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
>>>> implementing that and some work in videobuf2.
>>>>
>>>> Another thing is that V4L2 is very stream oriented. For most devices that's
>>>> fine as a lot of the parameters are not changeable during streaming,
>>>> especially if the pipeline is handled by multiple drivers. That said, for
>>>> devices that process data from memory to memory performing changes in the
>>>> media bus formats and pipeline configuration is not very efficient
>>>> currently, largely for the same reason.
>>>>
>>>> The request API that people have been working for a bit different use cases
>>>> isn't in mainline yet. It would allow more efficient per-request
>>>> configuration than what is currently possible, but it has turned out to be
>>>> far from trivial to implement.
>>>>
>>>>>  - validating processing parameters in V4l2 API is really complicated,
>>>>>    because the parameters (format, src&dest rectangles, rotation) are being
>>>>>    set incrementally, so we have to either allow some impossible,
>>>>> transitional
>>>>>    configurations or complicate the configuration steps even more (like
>>>>>    calling some ioctls multiple times for both input and output). In the end
>>>>>    all parameters have to be again validated just before performing the
>>>>>    operation.
>>>>
>>>> You have to validate the parameters in any case. In a MC pipeline this takes
>>>> place when the stream is started.
>>>>
>>>>>
>>>>> 3. generic approach (to add it to DRM core) has been rejected:
>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>
>>>> For GPUs I generally understand the reasoning: there's a very limited number
>>>> of users of this API --- primarily because it's not an application
>>>> interface.
>>>>
>>>> If you have a device that however falls under the scope of V4L2 (at least
>>>> API-wise), does this continue to be the case? Will there be only one or two
>>>> (or so) users for this API? Is it the case here?
>>>>
>>>> Using a device specific interface definitely has some benefits: there's no
>>>> need to think how would you generalise the interface for other similar
>>>> devices. There's no need to consider backwards compatibility as it's not a
>>>> requirement. The drawback is that the applications that need to support
>>>> similar devices will bear the burden of having to support different APIs.
>>>>
>>>> I don't mean to say that you should ram whatever under V4L2 / MC
>>>> independently of how unworkable that might be, but there are also clear
>>>> advantages in using a standardised interface such as V4L2.
>>>>
>>>> V4L2 has a long history behind it and if it was designed today, I bet it
>>>> would look quite different from what it is now.
>>>
>>> It's true. There is definitely a benefit with V4L2 because V4L2 provides Linux standard ABI - for DRM as of now not.
>>>
>>> However, I think that is a only benefit we could get through V4L2. Using V4L2 makes software stack of Platform to be complicated - We have to open video device node and card device node to display a image on the screen scaling or converting color space of the image and also we need to export DMA buffer from one side and import it to other side using DMABUF.
>>>
>>> It may not related to this but even V4L2 has performance problem - every QBUF/DQBUF requests performs mapping/unmapping DMA buffer you already know this. :)
>>>
>>> In addition, recently Display subsystems on ARM SoC tend to include pre/post processing hardware in Display controller - OMAP, Exynos8895 and MSM as long as I know.
>>>
>>
>> I agree with many of the arguments given by Inki above and earlier by
>> Marek. However, they apply to already existing V4L2 implementation,
>> not V4L2 as the idea in general, and I believe a comparison against a
>> complete new API that doesn't even exist in the kernel tree and
>> userspace yet (only in terms of patches on the list) is not fair.
>
> Below is a user space who uses Exynos DRM post processor driver, IPP driver.
> https://review.tizen.org/git/?p=platform/adaptation/samsung_exynos/libtdm-exynos.git;a=blob;f=src/tdm_exynos_pp.c;h=db20e6f226d313672d1d468e06d80526ea30121c;hb=refs/heads/tizen
>

Right, but the API is really Exynos-specific, while V4L2 is designed
from the start as a generic one and maintained as such.

> Marek patch series is just a new version of this driver which is specific to Exynos DRM. Marek is trying to enhance this driver.
> Ps. other DRM drivers in mainline already have such or similar API.

This kind of contradicts with response Marek received from DRM
community about his proposal. Which drivers in particular you have in
mind?

>
> We will also open the user space who uses new API later.

There is also already user space which uses V4L2 for this and V4L2
drivers for hardware similar to the one targeted by Marek's proposal,
including GStreamer support and iMX6 devices that Nicolas mentioned
before.

Best regards,
Tomasz

>
>
> Thanks,
> Inki Dae
>
>>
>> I strongly (if that's of any value) stand on Sakari's side and also
>> agree with DRM maintainers. V4L2 is already there, provides a general
>> interface for the userspace and already support the kind of devices
>> Marek mention. Sure, it might have several issues, but please give me
>> an example of a subsystem/interface/code that doesn't have any.
>> Instead of taking the easy (for short term) path, with a bit more
>> effort we can get something than in long run should end up much
>> better.
>>
>> Best regards,
>> Tomasz
>>
>>>
>>> Thanks,
>>> Inki Dae
>>>
>>>>
>>>>>
>>>>> 4. this api can be considered as extended 'blit' operation, other DRM
>>>>> drivers
>>>>>    (MGA, R128, VIA) already have ioctls for such operation, so there is also
>>>>>    place in DRM for it
>>>>
>>>> Added LMML to cc.
>>>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>>

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Inki Dae]

2017년 05월 10일 15:38에 Tomasz Figa 이(가) 쓴 글:
> On Wed, May 10, 2017 at 2:27 PM, Inki Dae <inki.dae@samsung.com> wrote:
>> Hi Tomasz,
>>
>> 2017년 05월 10일 14:38에 Tomasz Figa 이(가) 쓴 글:
>>> Hi Everyone,
>>>
>>> On Wed, May 10, 2017 at 9:24 AM, Inki Dae <inki.dae@samsung.com> wrote:
>>>>
>>>>
>>>> 2017년 04월 26일 07:21에 Sakari Ailus 이(가) 쓴 글:
>>>>> Hi Marek,
>>>>>
>>>>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>>>>>> Hi Laurent,
>>>>>>
>>>>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>>>>>> Hi Marek,
>>>>>>>
>>>>>>> (CC'ing Sakari Ailus)
>>>>>>>
>>>>>>> Thank you for the patches.
>>>>>>>
>>>>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>>>>>> Dear all,
>>>>>>>>
>>>>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>>>>>> support for hardware modules, which can be used for processing image data
>>>>>>> >from the one memory buffer to another. Typical memory-to-memory operations
>>>>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>>>>>> processors", which has been rejected as "not really needed in the DRM
>>>>>>>> core":
>>>>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>>>>
>>>>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>>>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>>>>>> with fbdev API.
>>>>>>>>
>>>>>>>> Here is a bit more information what picture processors are:
>>>>>>>>
>>>>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>>>>>> such operations. They can be used in paralel to the main GPU module to
>>>>>>>> offload CPU from processing grapics or video data. One of example use of
>>>>>>>> such modules is implementing video overlay, which usually requires color
>>>>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>>>>>> target window size.
>>>>>>>>
>>>>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>>>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>>>>>> picture processor (called pp for convenience). Such objects have a set of
>>>>>>>> standard DRM properties, which describes the operation to be performed by
>>>>>>>> respective hardware module. In typical case those properties are a source
>>>>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>>>>>> rectangle. Optionally a rotation property can be also specified if
>>>>>>>> supported by the given hardware. To perform an operation on image data,
>>>>>>>> userspace provides a set of properties and their values for given fbproc
>>>>>>>> object in a similar way as object and properties are provided for
>>>>>>>> performing atomic page flip / mode setting.
>>>>>>>>
>>>>>>>> The proposed API consists of the 3 new ioctls:
>>>>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>>>>>   processors,
>>>>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>>>>>   processor,
>>>>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>>>>>   property set.
>>>>>>>>
>>>>>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>>>>>> properties to add support for more advanced picture processing (for example
>>>>>>>> blending).
>>>>>>>>
>>>>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>>>>>> on the other side. It is also buggy, with significant design flaws - the
>>>>>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>>>>>> operations together with CRTC writeback and duplicating features, which
>>>>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>>>>>> rotator driver smaller by over 200 lines).
>>>>>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>>>>>> Stupid question, why DRM ?
>>>>>>
>>>>>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>>>>>
>>>>>> 1. we want to replace existing Exynos IPP subsystem:
>>>>>>  - it is used only in some internal/vendor trees, not in open-source
>>>>>>  - we want it to have sane and potentially extensible userspace API
>>>>>>  - but we don't want to loose its functionality
>>>>>>
>>>>>> 2. we want to have simple API for performing single image processing
>>>>>> operation:
>>>>>>  - typically it will be used by compositing window manager, this means that
>>>>>>    some parameters of the processing might change on each vblank (like
>>>>>>    destination rectangle for example). This api allows such change on each
>>>>>>    operation without any additional cost. V4L2 requires to reinitialize
>>>>>>    queues with new configuration on such change, what means that a bunch of
>>>>>>    ioctls has to be called.
>>>>>
>>>>> What do you mean by re-initialising the queue? Format, buffers or something
>>>>> else?
>>>>>
>>>>> If you need a larger buffer than what you have already allocated, you'll
>>>>> need to re-allocate, V4L2 or not.
>>>>>
>>>>> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
>>>>> implementing that and some work in videobuf2.
>>>>>
>>>>> Another thing is that V4L2 is very stream oriented. For most devices that's
>>>>> fine as a lot of the parameters are not changeable during streaming,
>>>>> especially if the pipeline is handled by multiple drivers. That said, for
>>>>> devices that process data from memory to memory performing changes in the
>>>>> media bus formats and pipeline configuration is not very efficient
>>>>> currently, largely for the same reason.
>>>>>
>>>>> The request API that people have been working for a bit different use cases
>>>>> isn't in mainline yet. It would allow more efficient per-request
>>>>> configuration than what is currently possible, but it has turned out to be
>>>>> far from trivial to implement.
>>>>>
>>>>>>  - validating processing parameters in V4l2 API is really complicated,
>>>>>>    because the parameters (format, src&dest rectangles, rotation) are being
>>>>>>    set incrementally, so we have to either allow some impossible,
>>>>>> transitional
>>>>>>    configurations or complicate the configuration steps even more (like
>>>>>>    calling some ioctls multiple times for both input and output). In the end
>>>>>>    all parameters have to be again validated just before performing the
>>>>>>    operation.
>>>>>
>>>>> You have to validate the parameters in any case. In a MC pipeline this takes
>>>>> place when the stream is started.
>>>>>
>>>>>>
>>>>>> 3. generic approach (to add it to DRM core) has been rejected:
>>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>
>>>>> For GPUs I generally understand the reasoning: there's a very limited number
>>>>> of users of this API --- primarily because it's not an application
>>>>> interface.
>>>>>
>>>>> If you have a device that however falls under the scope of V4L2 (at least
>>>>> API-wise), does this continue to be the case? Will there be only one or two
>>>>> (or so) users for this API? Is it the case here?
>>>>>
>>>>> Using a device specific interface definitely has some benefits: there's no
>>>>> need to think how would you generalise the interface for other similar
>>>>> devices. There's no need to consider backwards compatibility as it's not a
>>>>> requirement. The drawback is that the applications that need to support
>>>>> similar devices will bear the burden of having to support different APIs.
>>>>>
>>>>> I don't mean to say that you should ram whatever under V4L2 / MC
>>>>> independently of how unworkable that might be, but there are also clear
>>>>> advantages in using a standardised interface such as V4L2.
>>>>>
>>>>> V4L2 has a long history behind it and if it was designed today, I bet it
>>>>> would look quite different from what it is now.
>>>>
>>>> It's true. There is definitely a benefit with V4L2 because V4L2 provides Linux standard ABI - for DRM as of now not.
>>>>
>>>> However, I think that is a only benefit we could get through V4L2. Using V4L2 makes software stack of Platform to be complicated - We have to open video device node and card device node to display a image on the screen scaling or converting color space of the image and also we need to export DMA buffer from one side and import it to other side using DMABUF.
>>>>
>>>> It may not related to this but even V4L2 has performance problem - every QBUF/DQBUF requests performs mapping/unmapping DMA buffer you already know this. :)
>>>>
>>>> In addition, recently Display subsystems on ARM SoC tend to include pre/post processing hardware in Display controller - OMAP, Exynos8895 and MSM as long as I know.
>>>>
>>>
>>> I agree with many of the arguments given by Inki above and earlier by
>>> Marek. However, they apply to already existing V4L2 implementation,
>>> not V4L2 as the idea in general, and I believe a comparison against a
>>> complete new API that doesn't even exist in the kernel tree and
>>> userspace yet (only in terms of patches on the list) is not fair.
>>
>> Below is a user space who uses Exynos DRM post processor driver, IPP driver.
>> https://review.tizen.org/git/?p=platform/adaptation/samsung_exynos/libtdm-exynos.git;a=blob;f=src/tdm_exynos_pp.c;h=db20e6f226d313672d1d468e06d80526ea30121c;hb=refs/heads/tizen
>>
> 
> Right, but the API is really Exynos-specific, while V4L2 is designed
> from the start as a generic one and maintained as such.

As I mentioned before, I think this is only benefit we could get through V4L2.

> 
>> Marek patch series is just a new version of this driver which is specific to Exynos DRM. Marek is trying to enhance this driver.
>> Ps. other DRM drivers in mainline already have such or similar API.
> 
> This kind of contradicts with response Marek received from DRM
> community about his proposal. Which drivers in particular you have in
> mind?

You can check vmw_overlay_ioctl of vmwgfx driver and intel_overlay_put_image_ioctl of i915 driver. These was all I could find in mainline.
Seems the boundaries of whether we have to implement pre/post post processing mem2mem driver in V4L2 or DRM are really vague.


Thanks,
Inki Dae

> 
>>
>> We will also open the user space who uses new API later.
> 
> There is also already user space which uses V4L2 for this and V4L2
> drivers for hardware similar to the one targeted by Marek's proposal,
> including GStreamer support and iMX6 devices that Nicolas mentioned
> before.
> 
> Best regards,
> Tomasz
> 
>>
>>
>> Thanks,
>> Inki Dae
>>
>>>
>>> I strongly (if that's of any value) stand on Sakari's side and also
>>> agree with DRM maintainers. V4L2 is already there, provides a general
>>> interface for the userspace and already support the kind of devices
>>> Marek mention. Sure, it might have several issues, but please give me
>>> an example of a subsystem/interface/code that doesn't have any.
>>> Instead of taking the easy (for short term) path, with a bit more
>>> effort we can get something than in long run should end up much
>>> better.
>>>
>>> Best regards,
>>> Tomasz
>>>
>>>>
>>>> Thanks,
>>>> Inki Dae
>>>>
>>>>>
>>>>>>
>>>>>> 4. this api can be considered as extended 'blit' operation, other DRM
>>>>>> drivers
>>>>>>    (MGA, R128, VIA) already have ioctls for such operation, so there is also
>>>>>>    place in DRM for it
>>>>>
>>>>> Added LMML to cc.
>>>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>>
>>>
> 
> 
> 

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Daniel Vetter]

On Wed, May 10, 2017 at 12:29 PM, Inki Dae <inki.dae@samsung.com> wrote:
>> This kind of contradicts with response Marek received from DRM
>> community about his proposal. Which drivers in particular you have in
>> mind?
>
> You can check vmw_overlay_ioctl of vmwgfx driver and intel_overlay_put_image_ioctl of i915 driver. These was all I could find in mainline.
> Seems the boundaries of whether we have to implement pre/post post processing mem2mem driver in V4L2 or DRM are really vague.

These aren't picture processors, but overlay plane support merged
before we had the core drm overlay support. Please do not emulate them
at all, your patch will be rejected :-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Daniel Vetter]

On Wed, May 10, 2017 at 03:27:02PM +0900, Inki Dae wrote:
> Hi Tomasz,
> 
> 2017년 05월 10일 14:38에 Tomasz Figa 이(가) 쓴 글:
> > Hi Everyone,
> > 
> > On Wed, May 10, 2017 at 9:24 AM, Inki Dae <inki.dae@samsung.com> wrote:
> >>
> >>
> >> 2017년 04월 26일 07:21에 Sakari Ailus 이(가) 쓴 글:
> >>> Hi Marek,
> >>>
> >>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
> >>>> Hi Laurent,
> >>>>
> >>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
> >>>>> Hi Marek,
> >>>>>
> >>>>> (CC'ing Sakari Ailus)
> >>>>>
> >>>>> Thank you for the patches.
> >>>>>
> >>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
> >>>>>> Dear all,
> >>>>>>
> >>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
> >>>>>> support for hardware modules, which can be used for processing image data
> >>>>> >from the one memory buffer to another. Typical memory-to-memory operations
> >>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
> >>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
> >>>>>> processors", which has been rejected as "not really needed in the DRM
> >>>>>> core":
> >>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
> >>>>>>
> >>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
> >>>>>> will be specific only to Exynos DRM. I've also changed the name from
> >>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
> >>>>>> with fbdev API.
> >>>>>>
> >>>>>> Here is a bit more information what picture processors are:
> >>>>>>
> >>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
> >>>>>> such operations. They can be used in paralel to the main GPU module to
> >>>>>> offload CPU from processing grapics or video data. One of example use of
> >>>>>> such modules is implementing video overlay, which usually requires color
> >>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
> >>>>>> target window size.
> >>>>>>
> >>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
> >>>>>> based on DRM objects and their properties. A new DRM object is introduced:
> >>>>>> picture processor (called pp for convenience). Such objects have a set of
> >>>>>> standard DRM properties, which describes the operation to be performed by
> >>>>>> respective hardware module. In typical case those properties are a source
> >>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
> >>>>>> rectangle. Optionally a rotation property can be also specified if
> >>>>>> supported by the given hardware. To perform an operation on image data,
> >>>>>> userspace provides a set of properties and their values for given fbproc
> >>>>>> object in a similar way as object and properties are provided for
> >>>>>> performing atomic page flip / mode setting.
> >>>>>>
> >>>>>> The proposed API consists of the 3 new ioctls:
> >>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
> >>>>>>   processors,
> >>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
> >>>>>>   processor,
> >>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
> >>>>>>   property set.
> >>>>>>
> >>>>>> The proposed API is extensible. Drivers can attach their own, custom
> >>>>>> properties to add support for more advanced picture processing (for example
> >>>>>> blending).
> >>>>>>
> >>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
> >>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
> >>>>>> on the other side. It is also buggy, with significant design flaws - the
> >>>>>> biggest issue is the fact that the API covers memory-2-memory picture
> >>>>>> operations together with CRTC writeback and duplicating features, which
> >>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
> >>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
> >>>>>> rotator driver smaller by over 200 lines).
> >>>>> This seems to be the kind of hardware that is typically supported by V4L2.
> >>>>> Stupid question, why DRM ?
> >>>>
> >>>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
> >>>>
> >>>> 1. we want to replace existing Exynos IPP subsystem:
> >>>>  - it is used only in some internal/vendor trees, not in open-source
> >>>>  - we want it to have sane and potentially extensible userspace API
> >>>>  - but we don't want to loose its functionality
> >>>>
> >>>> 2. we want to have simple API for performing single image processing
> >>>> operation:
> >>>>  - typically it will be used by compositing window manager, this means that
> >>>>    some parameters of the processing might change on each vblank (like
> >>>>    destination rectangle for example). This api allows such change on each
> >>>>    operation without any additional cost. V4L2 requires to reinitialize
> >>>>    queues with new configuration on such change, what means that a bunch of
> >>>>    ioctls has to be called.
> >>>
> >>> What do you mean by re-initialising the queue? Format, buffers or something
> >>> else?
> >>>
> >>> If you need a larger buffer than what you have already allocated, you'll
> >>> need to re-allocate, V4L2 or not.
> >>>
> >>> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
> >>> implementing that and some work in videobuf2.
> >>>
> >>> Another thing is that V4L2 is very stream oriented. For most devices that's
> >>> fine as a lot of the parameters are not changeable during streaming,
> >>> especially if the pipeline is handled by multiple drivers. That said, for
> >>> devices that process data from memory to memory performing changes in the
> >>> media bus formats and pipeline configuration is not very efficient
> >>> currently, largely for the same reason.
> >>>
> >>> The request API that people have been working for a bit different use cases
> >>> isn't in mainline yet. It would allow more efficient per-request
> >>> configuration than what is currently possible, but it has turned out to be
> >>> far from trivial to implement.
> >>>
> >>>>  - validating processing parameters in V4l2 API is really complicated,
> >>>>    because the parameters (format, src&dest rectangles, rotation) are being
> >>>>    set incrementally, so we have to either allow some impossible,
> >>>> transitional
> >>>>    configurations or complicate the configuration steps even more (like
> >>>>    calling some ioctls multiple times for both input and output). In the end
> >>>>    all parameters have to be again validated just before performing the
> >>>>    operation.
> >>>
> >>> You have to validate the parameters in any case. In a MC pipeline this takes
> >>> place when the stream is started.
> >>>
> >>>>
> >>>> 3. generic approach (to add it to DRM core) has been rejected:
> >>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
> >>>
> >>> For GPUs I generally understand the reasoning: there's a very limited number
> >>> of users of this API --- primarily because it's not an application
> >>> interface.
> >>>
> >>> If you have a device that however falls under the scope of V4L2 (at least
> >>> API-wise), does this continue to be the case? Will there be only one or two
> >>> (or so) users for this API? Is it the case here?
> >>>
> >>> Using a device specific interface definitely has some benefits: there's no
> >>> need to think how would you generalise the interface for other similar
> >>> devices. There's no need to consider backwards compatibility as it's not a
> >>> requirement. The drawback is that the applications that need to support
> >>> similar devices will bear the burden of having to support different APIs.
> >>>
> >>> I don't mean to say that you should ram whatever under V4L2 / MC
> >>> independently of how unworkable that might be, but there are also clear
> >>> advantages in using a standardised interface such as V4L2.
> >>>
> >>> V4L2 has a long history behind it and if it was designed today, I bet it
> >>> would look quite different from what it is now.
> >>
> >> It's true. There is definitely a benefit with V4L2 because V4L2 provides Linux standard ABI - for DRM as of now not.
> >>
> >> However, I think that is a only benefit we could get through V4L2. Using V4L2 makes software stack of Platform to be complicated - We have to open video device node and card device node to display a image on the screen scaling or converting color space of the image and also we need to export DMA buffer from one side and import it to other side using DMABUF.
> >>
> >> It may not related to this but even V4L2 has performance problem - every QBUF/DQBUF requests performs mapping/unmapping DMA buffer you already know this. :)
> >>
> >> In addition, recently Display subsystems on ARM SoC tend to include pre/post processing hardware in Display controller - OMAP, Exynos8895 and MSM as long as I know.
> >>
> > 
> > I agree with many of the arguments given by Inki above and earlier by
> > Marek. However, they apply to already existing V4L2 implementation,
> > not V4L2 as the idea in general, and I believe a comparison against a
> > complete new API that doesn't even exist in the kernel tree and
> > userspace yet (only in terms of patches on the list) is not fair.
> 
> Below is a user space who uses Exynos DRM post processor driver, IPP driver.
> https://review.tizen.org/git/?p=platform/adaptation/samsung_exynos/libtdm-exynos.git;a=blob;f=src/tdm_exynos_pp.c;h=db20e6f226d313672d1d468e06d80526ea30121c;hb=refs/heads/tizen
> 
> Marek patch series is just a new version of this driver which is specific to Exynos DRM. Marek is trying to enhance this driver.
> Ps. other DRM drivers in mainline already have such or similar API.
> 
> We will also open the user space who uses new API later.

Those drivers are different, because they just expose a hw-specific abi.
Like the current IPP interfaces exposed by drm/exynos.

I think you have 2 options:
- Extend the current IPP interface in drm/exynos with whatever new pixel
  processor modes you want. Of course this still means you need to have
  the userspace side open-source, but otherwise it's all private to exynos
  hardware and software.

- If you want something standardized otoh, go with v4l2. And the issues
  you point out in v4l2 aren't uapi issues, but implementation details of
  the current vbuf helpers, which can be fixed. At least that's my
  understanding. And it should be fairly easy to fix that, simply switch
  from doing a map/unmap for every q/deqbuf to caching the mappings and
  use the stream dma-api interfaces to only do the flush (if needed at
  all, should turn into a no-op) on q/deqbuf.

Trying to come up with a generic drm api has imo not much chance of
getting accepted anytime soon (since for the simple pixel processor
pipeline it's just duplicating v4l, and for something more generic/faster
a generic interfaces is alwas too slow).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Inki Dae]

2017년 05월 10일 16:55에 Daniel Vetter 이(가) 쓴 글:
> On Wed, May 10, 2017 at 03:27:02PM +0900, Inki Dae wrote:
>> Hi Tomasz,
>>
>> 2017년 05월 10일 14:38에 Tomasz Figa 이(가) 쓴 글:
>>> Hi Everyone,
>>>
>>> On Wed, May 10, 2017 at 9:24 AM, Inki Dae <inki.dae@samsung.com> wrote:
>>>>
>>>>
>>>> 2017년 04월 26일 07:21에 Sakari Ailus 이(가) 쓴 글:
>>>>> Hi Marek,
>>>>>
>>>>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>>>>>> Hi Laurent,
>>>>>>
>>>>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>>>>>> Hi Marek,
>>>>>>>
>>>>>>> (CC'ing Sakari Ailus)
>>>>>>>
>>>>>>> Thank you for the patches.
>>>>>>>
>>>>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>>>>>> Dear all,
>>>>>>>>
>>>>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>>>>>> support for hardware modules, which can be used for processing image data
>>>>>>> >from the one memory buffer to another. Typical memory-to-memory operations
>>>>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>>>>>> processors", which has been rejected as "not really needed in the DRM
>>>>>>>> core":
>>>>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>>>>
>>>>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>>>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>>>>>> with fbdev API.
>>>>>>>>
>>>>>>>> Here is a bit more information what picture processors are:
>>>>>>>>
>>>>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>>>>>> such operations. They can be used in paralel to the main GPU module to
>>>>>>>> offload CPU from processing grapics or video data. One of example use of
>>>>>>>> such modules is implementing video overlay, which usually requires color
>>>>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>>>>>> target window size.
>>>>>>>>
>>>>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>>>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>>>>>> picture processor (called pp for convenience). Such objects have a set of
>>>>>>>> standard DRM properties, which describes the operation to be performed by
>>>>>>>> respective hardware module. In typical case those properties are a source
>>>>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>>>>>> rectangle. Optionally a rotation property can be also specified if
>>>>>>>> supported by the given hardware. To perform an operation on image data,
>>>>>>>> userspace provides a set of properties and their values for given fbproc
>>>>>>>> object in a similar way as object and properties are provided for
>>>>>>>> performing atomic page flip / mode setting.
>>>>>>>>
>>>>>>>> The proposed API consists of the 3 new ioctls:
>>>>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>>>>>   processors,
>>>>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>>>>>   processor,
>>>>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>>>>>   property set.
>>>>>>>>
>>>>>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>>>>>> properties to add support for more advanced picture processing (for example
>>>>>>>> blending).
>>>>>>>>
>>>>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>>>>>> on the other side. It is also buggy, with significant design flaws - the
>>>>>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>>>>>> operations together with CRTC writeback and duplicating features, which
>>>>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>>>>>> rotator driver smaller by over 200 lines).
>>>>>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>>>>>> Stupid question, why DRM ?
>>>>>>
>>>>>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>>>>>
>>>>>> 1. we want to replace existing Exynos IPP subsystem:
>>>>>>  - it is used only in some internal/vendor trees, not in open-source
>>>>>>  - we want it to have sane and potentially extensible userspace API
>>>>>>  - but we don't want to loose its functionality
>>>>>>
>>>>>> 2. we want to have simple API for performing single image processing
>>>>>> operation:
>>>>>>  - typically it will be used by compositing window manager, this means that
>>>>>>    some parameters of the processing might change on each vblank (like
>>>>>>    destination rectangle for example). This api allows such change on each
>>>>>>    operation without any additional cost. V4L2 requires to reinitialize
>>>>>>    queues with new configuration on such change, what means that a bunch of
>>>>>>    ioctls has to be called.
>>>>>
>>>>> What do you mean by re-initialising the queue? Format, buffers or something
>>>>> else?
>>>>>
>>>>> If you need a larger buffer than what you have already allocated, you'll
>>>>> need to re-allocate, V4L2 or not.
>>>>>
>>>>> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
>>>>> implementing that and some work in videobuf2.
>>>>>
>>>>> Another thing is that V4L2 is very stream oriented. For most devices that's
>>>>> fine as a lot of the parameters are not changeable during streaming,
>>>>> especially if the pipeline is handled by multiple drivers. That said, for
>>>>> devices that process data from memory to memory performing changes in the
>>>>> media bus formats and pipeline configuration is not very efficient
>>>>> currently, largely for the same reason.
>>>>>
>>>>> The request API that people have been working for a bit different use cases
>>>>> isn't in mainline yet. It would allow more efficient per-request
>>>>> configuration than what is currently possible, but it has turned out to be
>>>>> far from trivial to implement.
>>>>>
>>>>>>  - validating processing parameters in V4l2 API is really complicated,
>>>>>>    because the parameters (format, src&dest rectangles, rotation) are being
>>>>>>    set incrementally, so we have to either allow some impossible,
>>>>>> transitional
>>>>>>    configurations or complicate the configuration steps even more (like
>>>>>>    calling some ioctls multiple times for both input and output). In the end
>>>>>>    all parameters have to be again validated just before performing the
>>>>>>    operation.
>>>>>
>>>>> You have to validate the parameters in any case. In a MC pipeline this takes
>>>>> place when the stream is started.
>>>>>
>>>>>>
>>>>>> 3. generic approach (to add it to DRM core) has been rejected:
>>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>
>>>>> For GPUs I generally understand the reasoning: there's a very limited number
>>>>> of users of this API --- primarily because it's not an application
>>>>> interface.
>>>>>
>>>>> If you have a device that however falls under the scope of V4L2 (at least
>>>>> API-wise), does this continue to be the case? Will there be only one or two
>>>>> (or so) users for this API? Is it the case here?
>>>>>
>>>>> Using a device specific interface definitely has some benefits: there's no
>>>>> need to think how would you generalise the interface for other similar
>>>>> devices. There's no need to consider backwards compatibility as it's not a
>>>>> requirement. The drawback is that the applications that need to support
>>>>> similar devices will bear the burden of having to support different APIs.
>>>>>
>>>>> I don't mean to say that you should ram whatever under V4L2 / MC
>>>>> independently of how unworkable that might be, but there are also clear
>>>>> advantages in using a standardised interface such as V4L2.
>>>>>
>>>>> V4L2 has a long history behind it and if it was designed today, I bet it
>>>>> would look quite different from what it is now.
>>>>
>>>> It's true. There is definitely a benefit with V4L2 because V4L2 provides Linux standard ABI - for DRM as of now not.
>>>>
>>>> However, I think that is a only benefit we could get through V4L2. Using V4L2 makes software stack of Platform to be complicated - We have to open video device node and card device node to display a image on the screen scaling or converting color space of the image and also we need to export DMA buffer from one side and import it to other side using DMABUF.
>>>>
>>>> It may not related to this but even V4L2 has performance problem - every QBUF/DQBUF requests performs mapping/unmapping DMA buffer you already know this. :)
>>>>
>>>> In addition, recently Display subsystems on ARM SoC tend to include pre/post processing hardware in Display controller - OMAP, Exynos8895 and MSM as long as I know.
>>>>
>>>
>>> I agree with many of the arguments given by Inki above and earlier by
>>> Marek. However, they apply to already existing V4L2 implementation,
>>> not V4L2 as the idea in general, and I believe a comparison against a
>>> complete new API that doesn't even exist in the kernel tree and
>>> userspace yet (only in terms of patches on the list) is not fair.
>>
>> Below is a user space who uses Exynos DRM post processor driver, IPP driver.
>> https://review.tizen.org/git/?p=platform/adaptation/samsung_exynos/libtdm-exynos.git;a=blob;f=src/tdm_exynos_pp.c;h=db20e6f226d313672d1d468e06d80526ea30121c;hb=refs/heads/tizen
>>
>> Marek patch series is just a new version of this driver which is specific to Exynos DRM. Marek is trying to enhance this driver.
>> Ps. other DRM drivers in mainline already have such or similar API.
>>
>> We will also open the user space who uses new API later.
> 
> Those drivers are different, because they just expose a hw-specific abi.
> Like the current IPP interfaces exposed by drm/exynos.
> 
> I think you have 2 options:
> - Extend the current IPP interface in drm/exynos with whatever new pixel
>   processor modes you want. Of course this still means you need to have

Yes, this is only thing we could select as of now.


Thanks,
Inki Dae


>   the userspace side open-source, but otherwise it's all private to exynos
>   hardware and software.
> 
> - If you want something standardized otoh, go with v4l2. And the issues
>   you point out in v4l2 aren't uapi issues, but implementation details of
>   the current vbuf helpers, which can be fixed. At least that's my
>   understanding. And it should be fairly easy to fix that, simply switch
>   from doing a map/unmap for every q/deqbuf to caching the mappings and
>   use the stream dma-api interfaces to only do the flush (if needed at
>   all, should turn into a no-op) on q/deqbuf.
> 
> Trying to come up with a generic drm api has imo not much chance of
> getting accepted anytime soon (since for the simple pixel processor
> pipeline it's just duplicating v4l, and for something more generic/faster
> a generic interfaces is alwas too slow).
> -Daniel
> 

Re: [RFC 0/4] Exynos DRM: add Picture Processor extension

[Marek Szyprowski]

Hi Daniel,

On 2017-05-10 09:55, Daniel Vetter wrote:
> On Wed, May 10, 2017 at 03:27:02PM +0900, Inki Dae wrote:
>> Hi Tomasz,
>>
>> 2017년 05월 10일 14:38에 Tomasz Figa 이(가) 쓴 글:
>>> Hi Everyone,
>>>
>>> On Wed, May 10, 2017 at 9:24 AM, Inki Dae <inki.dae@samsung.com> wrote:
>>>>
>>>> 2017년 04월 26일 07:21에 Sakari Ailus 이(가) 쓴 글:
>>>>> Hi Marek,
>>>>>
>>>>> On Thu, Apr 20, 2017 at 01:23:09PM +0200, Marek Szyprowski wrote:
>>>>>> Hi Laurent,
>>>>>>
>>>>>> On 2017-04-20 12:25, Laurent Pinchart wrote:
>>>>>>> Hi Marek,
>>>>>>>
>>>>>>> (CC'ing Sakari Ailus)
>>>>>>>
>>>>>>> Thank you for the patches.
>>>>>>>
>>>>>>> On Thursday 20 Apr 2017 11:13:36 Marek Szyprowski wrote:
>>>>>>>> Dear all,
>>>>>>>>
>>>>>>>> This is an updated proposal for extending EXYNOS DRM API with generic
>>>>>>>> support for hardware modules, which can be used for processing image data
>>>>>>> >from the one memory buffer to another. Typical memory-to-memory operations
>>>>>>>> are: rotation, scaling, colour space conversion or mix of them. This is a
>>>>>>>> follow-up of my previous proposal "[RFC 0/2] New feature: Framebuffer
>>>>>>>> processors", which has been rejected as "not really needed in the DRM
>>>>>>>> core":
>>>>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>>>>>
>>>>>>>> In this proposal I moved all the code to Exynos DRM driver, so now this
>>>>>>>> will be specific only to Exynos DRM. I've also changed the name from
>>>>>>>> framebuffer processor (fbproc) to picture processor (pp) to avoid confusion
>>>>>>>> with fbdev API.
>>>>>>>>
>>>>>>>> Here is a bit more information what picture processors are:
>>>>>>>>
>>>>>>>> Embedded SoCs are known to have a number of hardware blocks, which perform
>>>>>>>> such operations. They can be used in paralel to the main GPU module to
>>>>>>>> offload CPU from processing grapics or video data. One of example use of
>>>>>>>> such modules is implementing video overlay, which usually requires color
>>>>>>>> space conversion from NV12 (or similar) to RGB32 color space and scaling to
>>>>>>>> target window size.
>>>>>>>>
>>>>>>>> The proposed API is heavily inspired by atomic KMS approach - it is also
>>>>>>>> based on DRM objects and their properties. A new DRM object is introduced:
>>>>>>>> picture processor (called pp for convenience). Such objects have a set of
>>>>>>>> standard DRM properties, which describes the operation to be performed by
>>>>>>>> respective hardware module. In typical case those properties are a source
>>>>>>>> fb id and rectangle (x, y, width, height) and destination fb id and
>>>>>>>> rectangle. Optionally a rotation property can be also specified if
>>>>>>>> supported by the given hardware. To perform an operation on image data,
>>>>>>>> userspace provides a set of properties and their values for given fbproc
>>>>>>>> object in a similar way as object and properties are provided for
>>>>>>>> performing atomic page flip / mode setting.
>>>>>>>>
>>>>>>>> The proposed API consists of the 3 new ioctls:
>>>>>>>> - DRM_IOCTL_EXYNOS_PP_GET_RESOURCES: to enumerate all available picture
>>>>>>>>    processors,
>>>>>>>> - DRM_IOCTL_EXYNOS_PP_GET: to query capabilities of given picture
>>>>>>>>    processor,
>>>>>>>> - DRM_IOCTL_EXYNOS_PP_COMMIT: to perform operation described by given
>>>>>>>>    property set.
>>>>>>>>
>>>>>>>> The proposed API is extensible. Drivers can attach their own, custom
>>>>>>>> properties to add support for more advanced picture processing (for example
>>>>>>>> blending).
>>>>>>>>
>>>>>>>> This proposal aims to replace Exynos DRM IPP (Image Post Processing)
>>>>>>>> subsystem. IPP API is over-engineered in general, but not really extensible
>>>>>>>> on the other side. It is also buggy, with significant design flaws - the
>>>>>>>> biggest issue is the fact that the API covers memory-2-memory picture
>>>>>>>> operations together with CRTC writeback and duplicating features, which
>>>>>>>> belongs to video plane. Comparing with IPP subsystem, the PP framework is
>>>>>>>> smaller (1807 vs 778 lines) and allows driver simplification (Exynos
>>>>>>>> rotator driver smaller by over 200 lines).
>>>>>>> This seems to be the kind of hardware that is typically supported by V4L2.
>>>>>>> Stupid question, why DRM ?
>>>>>> Let me elaborate a bit on the reasons for implementing it in Exynos DRM:
>>>>>>
>>>>>> 1. we want to replace existing Exynos IPP subsystem:
>>>>>>   - it is used only in some internal/vendor trees, not in open-source
>>>>>>   - we want it to have sane and potentially extensible userspace API
>>>>>>   - but we don't want to loose its functionality
>>>>>>
>>>>>> 2. we want to have simple API for performing single image processing
>>>>>> operation:
>>>>>>   - typically it will be used by compositing window manager, this means that
>>>>>>     some parameters of the processing might change on each vblank (like
>>>>>>     destination rectangle for example). This api allows such change on each
>>>>>>     operation without any additional cost. V4L2 requires to reinitialize
>>>>>>     queues with new configuration on such change, what means that a bunch of
>>>>>>     ioctls has to be called.
>>>>> What do you mean by re-initialising the queue? Format, buffers or something
>>>>> else?
>>>>>
>>>>> If you need a larger buffer than what you have already allocated, you'll
>>>>> need to re-allocate, V4L2 or not.
>>>>>
>>>>> We also do lack a way to destroy individual buffers in V4L2. It'd be up to
>>>>> implementing that and some work in videobuf2.
>>>>>
>>>>> Another thing is that V4L2 is very stream oriented. For most devices that's
>>>>> fine as a lot of the parameters are not changeable during streaming,
>>>>> especially if the pipeline is handled by multiple drivers. That said, for
>>>>> devices that process data from memory to memory performing changes in the
>>>>> media bus formats and pipeline configuration is not very efficient
>>>>> currently, largely for the same reason.
>>>>>
>>>>> The request API that people have been working for a bit different use cases
>>>>> isn't in mainline yet. It would allow more efficient per-request
>>>>> configuration than what is currently possible, but it has turned out to be
>>>>> far from trivial to implement.
>>>>>
>>>>>>   - validating processing parameters in V4l2 API is really complicated,
>>>>>>     because the parameters (format, src&dest rectangles, rotation) are being
>>>>>>     set incrementally, so we have to either allow some impossible,
>>>>>> transitional
>>>>>>     configurations or complicate the configuration steps even more (like
>>>>>>     calling some ioctls multiple times for both input and output). In the end
>>>>>>     all parameters have to be again validated just before performing the
>>>>>>     operation.
>>>>> You have to validate the parameters in any case. In a MC pipeline this takes
>>>>> place when the stream is started.
>>>>>
>>>>>> 3. generic approach (to add it to DRM core) has been rejected:
>>>>>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg146286.html
>>>>> For GPUs I generally understand the reasoning: there's a very limited number
>>>>> of users of this API --- primarily because it's not an application
>>>>> interface.
>>>>>
>>>>> If you have a device that however falls under the scope of V4L2 (at least
>>>>> API-wise), does this continue to be the case? Will there be only one or two
>>>>> (or so) users for this API? Is it the case here?
>>>>>
>>>>> Using a device specific interface definitely has some benefits: there's no
>>>>> need to think how would you generalise the interface for other similar
>>>>> devices. There's no need to consider backwards compatibility as it's not a
>>>>> requirement. The drawback is that the applications that need to support
>>>>> similar devices will bear the burden of having to support different APIs.
>>>>>
>>>>> I don't mean to say that you should ram whatever under V4L2 / MC
>>>>> independently of how unworkable that might be, but there are also clear
>>>>> advantages in using a standardised interface such as V4L2.
>>>>>
>>>>> V4L2 has a long history behind it and if it was designed today, I bet it
>>>>> would look quite different from what it is now.
>>>> It's true. There is definitely a benefit with V4L2 because V4L2 provides Linux standard ABI - for DRM as of now not.
>>>>
>>>> However, I think that is a only benefit we could get through V4L2. Using V4L2 makes software stack of Platform to be complicated - We have to open video device node and card device node to display a image on the screen scaling or converting color space of the image and also we need to export DMA buffer from one side and import it to other side using DMABUF.
>>>>
>>>> It may not related to this but even V4L2 has performance problem - every QBUF/DQBUF requests performs mapping/unmapping DMA buffer you already know this. :)
>>>>
>>>> In addition, recently Display subsystems on ARM SoC tend to include pre/post processing hardware in Display controller - OMAP, Exynos8895 and MSM as long as I know.
>>>>
>>> I agree with many of the arguments given by Inki above and earlier by
>>> Marek. However, they apply to already existing V4L2 implementation,
>>> not V4L2 as the idea in general, and I believe a comparison against a
>>> complete new API that doesn't even exist in the kernel tree and
>>> userspace yet (only in terms of patches on the list) is not fair.
>> Below is a user space who uses Exynos DRM post processor driver, IPP driver.
>> https://review.tizen.org/git/?p=platform/adaptation/samsung_exynos/libtdm-exynos.git;a=blob;f=src/tdm_exynos_pp.c;h=db20e6f226d313672d1d468e06d80526ea30121c;hb=refs/heads/tizen
>>
>> Marek patch series is just a new version of this driver which is specific to Exynos DRM. Marek is trying to enhance this driver.
>> Ps. other DRM drivers in mainline already have such or similar API.
>>
>> We will also open the user space who uses new API later.
> Those drivers are different, because they just expose a hw-specific abi.
> Like the current IPP interfaces exposed by drm/exynos.
>
> I think you have 2 options:
> - Extend the current IPP interface in drm/exynos with whatever new pixel
>    processor modes you want. Of course this still means you need to have
>    the userspace side open-source, but otherwise it's all private to exynos
>    hardware and software.

That's what I proposed in RFC v2 posted 2 days ago - everything is kept in
Exynos DRM driver, no changes to DRM-core at all. Maybe calling it Exynos
IPP v2 would have been a better idea.

> - If you want something standardized otoh, go with v4l2. And the issues
>    you point out in v4l2 aren't uapi issues, but implementation details of
>    the current vbuf helpers, which can be fixed. At least that's my
>    understanding. And it should be fairly easy to fix that, simply switch
>    from doing a map/unmap for every q/deqbuf to caching the mappings and
>    use the stream dma-api interfaces to only do the flush (if needed at
>    all, should turn into a no-op) on q/deqbuf.
>
> Trying to come up with a generic drm api has imo not much chance of
> getting accepted anytime soon (since for the simple pixel processor
> pipeline it's just duplicating v4l, and for something more generic/faster
> a generic interfaces is alwas too slow).

Okay, I don't want to make it DRM-wide. For us it is enough to have it at
Exynos DRM, like existing IPP ioctls.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland